Lactoferrin
Encyclopedia
Lactoferrin also known as lactotransferrin (LTF), is a multifunctional protein
of the transferrin
family. Lactoferrin is a globular glycoprotein
with a molecular mass of about 80 kDa
that is widely represented in various secretory fluids, such as milk
, saliva
, tears
, and nasal secretions
. Lactoferrin is also present in secondary granules of PMN
and is secreted by some acinar cells
. Lactoferrin can be purified from milk or produced recombinantly
. Human colostrum
("first milk") has the highest concentration, followed by human milk, then cow milk (150 mg/L).
Lactoferrin is one of the components of the immune system
of the body; it has antimicrobial activity (bacteriocide
, fungicide
) and is part of the innate defense, mainly at mucoses. In particular, lactoferrin provides antibacterial
activity to human infants. Lactoferrin interacts with DNA
and RNA
, polysaccharides and heparin
, and shows some of its biological functions in complexes with these ligand
s.
, optical absorption spectra and presence of two iron atoms per protein molecule. The protein was extracted from milk, contained iron and was structurally and chemically similar to serum
transferrin
. Therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. Also in 1961, the antibacterial action of lactoferrin has been documented and associated with its ability to bind iron.
to the cells and control the level of free iron in the blood and external secretions. It is present in the milk of humans and other mammals, in the blood plasma
and neutrophils and is one of the major proteins of virtually all exocrine secretions of mammals, such as saliva
, gall
, tears
and pancreas
. Concentration of lactoferrin in the milk varies from 7 g/L in the colostrum
to 1 g/L in mature milk.
X-ray diffraction
reveals that lactoferrin is based on one polypeptide chain that contains about 700 amino acids and forms two homologous globular domains
named N-and C-lobes. N-lobe corresponds to amino acid residues 1-333 and C-lobe to 345-692, and the ends of those domains are connected by a short α-helix. Each lobe consists of two subdomains, N1, N2 and C1, C2, and contains one iron binding site and one glycosylation
site. The degree of glycosylation of the protein may be different and therefore the molecular weight of lactoferrin varies between 76 and 80 kDa. The stability of lactoferrin has been associated with the high glycosylation degree.
Lactoferrin belongs to the basic proteins, its isoelectric point
is 8.7. It exists in two forms: iron-rich hololactoferrin and iron-free apolactoferrin. Their tertiary structures are different; apolactoferrin is characterized by "open" conformation of the N-lobe and the "closed" conformation of the C-lobe, and both lobes are closed in the hololactoferrin.
Each lactoferrin molecule can reversibly bind two ions of iron, zinc
, copper
or other metals. The binding sites are localized in each of the two protein globules. There, each ion is bonded with six ligands: four from the polypeptide chain (two tyrosine
residues, one histidine
residue and one aspartic acid
residue) and two from carbonate
or bicarbonate
ions.
Lactoferrin forms reddish complex with iron; its affinity for iron is 300 times higher than that of transferrin
. The affinity increases in weakly acidic medium. This facilitates the transfer of iron from transferrin to lactoferrin during inflammation
s, when the pH of tissues decreases due to accumulation of lactic
and other acids. The saturated iron concentration in lactoferrin in human milk is estimated as 10 to 30% (100% corresponds to all lactoferrin molecules containing 2 iron atoms). It is demonstrated that lactoferrin is involved not only in the transport of iron, zinc and copper, but also in the regulation of their intake. Presence of loose ions of zinc and copper does not affect the iron binding ability of lactoferrin, and might even increase it.
s to tetramer
s. Lactoferrin tends to polymerize both in vitro and in vivo, especially at high concentrations. Several authors found that the dominant form of lactoferrin in physiological conditions is a tetramer, with the monomer:tetramer ratio of 1:4 at the protein concentrations of 10−5 M.
It is suggested that the oligomer
state of lactoferrin is determined by its concentration and that polymerization
of lactoferrin is strongly affected by the presence of Ca2+ ions. In particular, monomers were dominant at concentrations below 10−10−10−11 M in the presence of Ca2+, but they converted into tetramers at lactoferrin concentrations above 10−9−10−10 M. Titer
of lactoferrin in the blood corresponds to this particular "transition concentration" and thus lactoferrin in the blood should be presented both as a monomer and tetramer. Many functional properties of lactoferrin depend on its oligomeric state. In particular, monomeric, but not tetrameric lactoferrin can strongly bind to DNA.
. Apart from its main biological function, namely binding and transport of iron ions, lactoferrin also has antibacterial, antiviral, antiparasitic, catalytic, anti-cancer, anti-allergic and radioprotecting functions and properties.
s on the cell surface of microorganisms. Lactoferrin binds to lipopolysaccharide of bacterial walls, and the oxidized iron part of the lactoferrin oxidizes bacteria via formation of peroxide
s. This affects the membrane permeability and results in the cell breakdown (lysis
).
Although lactoferrin also has other antibacterial mechanisms not related to iron, such as stimulation of phagocytosis, the interaction with the outer bacterial membrane described above is the most dominant and most studied. Lactoferrin not only disrupts the membrane, but even penetrates into the cell. Its binding to the bacteria wall is associated with the specific peptide
lactoferricin
, which is located at the N-lobe of lactoferrin and is produced by in vitro cleavage of lactoferrin with another protein, trypsin
. A mechanism of the antimicrobial action of lactoferrin has been reported as lactoferrin targets H(+)-ATPase and interferes with proton translocation in the cell membrane, resulting in a lethal effect in vitro.
s, including the herpes simplex virus
1 and 2, cytomegalovirus
, HIV
, hepatitis C virus
, hantavirus
es, rotavirus
es, poliovirus
type 1, human respiratory syncytial virus
and murine leukemia virus
es.
The most studied mechanism of antiviral activity of lactoferrin is its diversion of virus particles from the target cells. Many viruses tend to bind to the lipoprotein
s of the cell membranes and then penetrate into the cell. Lactoferrin binds to the same lipoproteins thereby repelling the virus particles. Iron-free apolactoferrin is more efficient in this function than hololactoferrin; and lactoferricin, which is responsible for antimicrobial properties of lactoferrin, shows almost no antiviral activity.
Beside interacting with the cell walls, lactoferrin also directly binds to viral particles, such as the hepatitis
viruses. This mechanism is also confirmed by the antiviral activity of lactoferrin against rotaviruses, which act on different cell types.
Lactoferrin also suppresses virus replication after the virus penetrated into the cell. Such an indirect antiviral effect is achieved by affecting natural killer cell
s, granulocyte
s and macrophage
s – cells, which play a crucial role in the early stages of viral infections, such as severe acute respiratory syndrome
(SARS).
– a diploid fungus
(a form of yeast
) that causes opportunistic
oral and genital infections in humans. Fluconazole
has long been used against Candida albicans, which resulted in emergence of strains
resistant to this drug. However, a combination of lactoferrin with fluconazole can act against fluconazole-resistant strains of Candida albicans as well as other types of Candida
: C. glabrata, C. krusei, C. parapsilosis and C. tropicalis. Antifungal activity is observed for sequential incubation of Candida with lactoferrin and then with fluconazole, but not vice versa. The antifungal activity of lactoferricin exceeds that of lactoferrin. In particular, synthetic peptide 1-11 lactoferricin shows much greater activity against Candida albicans than native lactoferricin.
Administration of lactoferrin through drinking water to mice with weakened immune systems and symptoms of aphthous ulcer
reduced the number of Candida albicans strains in the mouth and the size of the damaged areas in the tongue. Oral administration of lactoferrin to animals also reduced the number of pathogenic organisms in the tissues close to the gastrointestinal tract
. Candida albicans could also be completely eradicated with a mixture containing lactoferrin, lysozyme
and introakonazol in HIV-positive patients who were resistant to other antifungal drugs. Such antifungal action when other drugs deem inefficient is characteristic of lactoferrin and is especially valuable for HIV-infected patients. Contrary to the antiviral and antibacterial actions of lactoferrin, very little is known about the mechanism of its antifungal action. Lactoferrin seems to destroy the cell wall and bind the plasma membrane of C. albicans.
besides, the protein preferably binds to the double-stranded than to the single-stranded DNA. The ability of lactoferrin to bind DNA is used for the isolation and purification of lactoferrin using affinity chromatography
with columns containing immobilized DNA-containing sorbent
s, such as agarose with the immobilized single-stranded DNA.
and exhibits the properties of pyrimidine
-specific secretory ribonuclease
s. In particular, by destroying the RNA genome, milk RNase inhibits reverse transcription of retrovirus
es that cause breast cancer
in mice. Parsi
women in West India
have the milk RNase level markedly lower than in other groups, and their breast cancer
rate is three times higher than average. Thus, ribonuclease
s of milk, and lactoferrin in particular, might play an important role in pathogenesis
of diseases caused by various retrovirus
es.
is TAA, and TGA in Mus musculus. Deletions, insertions and mutations of stop codons affect the coding part and its length varies between 2,055 and 2,190 nucleotide
pairs. Gene polymorphism between species is much more diverse than the intraspecific polymorphism of lactoferrin. There are differences in amino acid sequences: 8 in Homo sapiens, 6 in Mus musculus, 6 in Capra hircus, 10 in Bos taurus and 20 in Sus scrofa. This variation may indicate functional differences between different types of lactoferrin.
In humans, lactoferrin gene LTF is located on the third chromosome
in the locus
3q21-q23. In ox
en, the coding sequence consists of 17 exon
s and has a length of about 34,500 nucleotide
pairs. Exons of the lactoferrin gene in oxen have a similar size to the exons of other genes of the transferrin
family, whereas the sizes of introns differ within the family. Similarity in the size of exons and their distribution in the domains of the protein molecule indicates that the evolutionary development of lactoferrin gene occurred by duplication. Study of polymorphism of genes that encode lactoferrin helps selecting livestock breeds that are resistant to mastitis
.
plays an important role in the internalization
of lactoferrin; it also facilitates absorption of iron ions by lactoferrin. It was shown that gene expression
increases with age in the duodenum
and decreases in the jejunum
.
and lactoferrin, while hypothiocyanite is missing in cystic fibrosis
patients. Lactoferrin, a component of innate immunity, prevents bacterial biofilm
development. The loss of microbicidal activity and increased formation of biofilm due to decreased lactoferrin activity is observed in patients with cystic fibrosis. These findings demonstrate the important role of lactoferrin in human host defense and especially in lung.
Lactoferrin with hypothiocyanite has been granted orphan drug
status by the EMEA
and the FDA.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
of the transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...
family. Lactoferrin is a globular glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
with a molecular mass of about 80 kDa
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
that is widely represented in various secretory fluids, such as milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
, saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
, tears
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....
, and nasal secretions
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
. Lactoferrin is also present in secondary granules of PMN
Neutrophil granulocyte
Neutrophil granulocytes are the most abundant type of white blood cells in mammals and form an essential part of the innate immune system. They are generally referred to as either neutrophils or polymorphonuclear neutrophils , and are subdivided into segmented neutrophils and banded neutrophils...
and is secreted by some acinar cells
Centroacinar cells
Centroacinar cells are spindle-shaped cells in the exocrine pancreas. Centroacinar cells are an extension of the intercalated duct cells into each pancreatic acinus. The intercalated ducts take the bicarbonate to intralobular ducts which become lobular ducts...
. Lactoferrin can be purified from milk or produced recombinantly
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
. Human colostrum
Colostrum
Colostrum is a form of milk produced by the mammary glands of mammals in late pregnancy. Most species will generate colostrum just prior to giving birth...
("first milk") has the highest concentration, followed by human milk, then cow milk (150 mg/L).
Lactoferrin is one of the components of the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
of the body; it has antimicrobial activity (bacteriocide
Bacteriocide
A bactericide or bacteriocide, abbreviated Bcidal, is a substance that kills bacteria and, ideally, nothing else. Bactericides are disinfectants, antiseptics or antibiotics.-Bactericidal disinfectants:...
, fungicide
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
) and is part of the innate defense, mainly at mucoses. In particular, lactoferrin provides antibacterial
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
activity to human infants. Lactoferrin interacts with DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
, polysaccharides and heparin
Heparin
Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...
, and shows some of its biological functions in complexes with these ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s.
History
Occurrence of iron-containing red protein in bovine milk was reported as early as in 1939; however, the protein could not be properly characterized because it could not be extracted with sufficient purity. Its first detailed studies were reported around 1960. They documented the molecular weight, isoelectric pointIsoelectric point
The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....
, optical absorption spectra and presence of two iron atoms per protein molecule. The protein was extracted from milk, contained iron and was structurally and chemically similar to serum
Blood serum
In blood, the serum is the component that is neither a blood cell nor a clotting factor; it is the blood plasma with the fibrinogens removed...
transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...
. Therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. Also in 1961, the antibacterial action of lactoferrin has been documented and associated with its ability to bind iron.
Molecular structure
Lactoferrin is one of the transferrin proteins that transfer ironIron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
to the cells and control the level of free iron in the blood and external secretions. It is present in the milk of humans and other mammals, in the blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
and neutrophils and is one of the major proteins of virtually all exocrine secretions of mammals, such as saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
, gall
Gall
Galls or cecidia are outgrowths on the surface of lifeforms caused by invasion by other lifeforms, such as parasites or bacterial infection. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites...
, tears
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....
and pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
. Concentration of lactoferrin in the milk varies from 7 g/L in the colostrum
Colostrum
Colostrum is a form of milk produced by the mammary glands of mammals in late pregnancy. Most species will generate colostrum just prior to giving birth...
to 1 g/L in mature milk.
X-ray diffraction
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
reveals that lactoferrin is based on one polypeptide chain that contains about 700 amino acids and forms two homologous globular domains
Protein domain
A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...
named N-and C-lobes. N-lobe corresponds to amino acid residues 1-333 and C-lobe to 345-692, and the ends of those domains are connected by a short α-helix. Each lobe consists of two subdomains, N1, N2 and C1, C2, and contains one iron binding site and one glycosylation
Glycosylation
Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule . In biology glycosylation refers to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules...
site. The degree of glycosylation of the protein may be different and therefore the molecular weight of lactoferrin varies between 76 and 80 kDa. The stability of lactoferrin has been associated with the high glycosylation degree.
Lactoferrin belongs to the basic proteins, its isoelectric point
Isoelectric point
The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....
is 8.7. It exists in two forms: iron-rich hololactoferrin and iron-free apolactoferrin. Their tertiary structures are different; apolactoferrin is characterized by "open" conformation of the N-lobe and the "closed" conformation of the C-lobe, and both lobes are closed in the hololactoferrin.
Each lactoferrin molecule can reversibly bind two ions of iron, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
or other metals. The binding sites are localized in each of the two protein globules. There, each ion is bonded with six ligands: four from the polypeptide chain (two tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
residues, one histidine
Histidine
Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...
residue and one aspartic acid
Aspartic acid
Aspartic acid is an α-amino acid with the chemical formula HOOCCHCH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins...
residue) and two from carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
or bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
ions.
Lactoferrin forms reddish complex with iron; its affinity for iron is 300 times higher than that of transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...
. The affinity increases in weakly acidic medium. This facilitates the transfer of iron from transferrin to lactoferrin during inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
s, when the pH of tissues decreases due to accumulation of lactic
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
and other acids. The saturated iron concentration in lactoferrin in human milk is estimated as 10 to 30% (100% corresponds to all lactoferrin molecules containing 2 iron atoms). It is demonstrated that lactoferrin is involved not only in the transport of iron, zinc and copper, but also in the regulation of their intake. Presence of loose ions of zinc and copper does not affect the iron binding ability of lactoferrin, and might even increase it.
Polymeric forms
Both in blood plasma and in secretory fluids lactoferrin can exist in different polymeric forms ranging from monomerMonomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
s to tetramer
Tetramer
A tetramer is a protein with four subunits . There are homotetramers such as glutathione S-transferase or single-strand binding protein, dimers of hetero-dimers such as hemoglobin , and heterotetramers, where each subunit is different.-Subunit interactions in tetramers:The interactions between...
s. Lactoferrin tends to polymerize both in vitro and in vivo, especially at high concentrations. Several authors found that the dominant form of lactoferrin in physiological conditions is a tetramer, with the monomer:tetramer ratio of 1:4 at the protein concentrations of 10−5 M.
It is suggested that the oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
state of lactoferrin is determined by its concentration and that polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
of lactoferrin is strongly affected by the presence of Ca2+ ions. In particular, monomers were dominant at concentrations below 10−10−10−11 M in the presence of Ca2+, but they converted into tetramers at lactoferrin concentrations above 10−9−10−10 M. Titer
Titer
A titer is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive...
of lactoferrin in the blood corresponds to this particular "transition concentration" and thus lactoferrin in the blood should be presented both as a monomer and tetramer. Many functional properties of lactoferrin depend on its oligomeric state. In particular, monomeric, but not tetrameric lactoferrin can strongly bind to DNA.
Biological functions
Lactoferrin belongs to the innate immune systemInnate immune system
The innate immune system, also known as non-specific immune system and secondary line of defence, comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner...
. Apart from its main biological function, namely binding and transport of iron ions, lactoferrin also has antibacterial, antiviral, antiparasitic, catalytic, anti-cancer, anti-allergic and radioprotecting functions and properties.
Antibacterial activity
Antibacterial activity of lactoferrin is best studied; it originates from the iron-binding properties of lactoferrin, which deprive the bacterial flora from an element necessary for its growth. Antibacterial action of lactoferrin is also explained by the presence of specific receptorReceptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s on the cell surface of microorganisms. Lactoferrin binds to lipopolysaccharide of bacterial walls, and the oxidized iron part of the lactoferrin oxidizes bacteria via formation of peroxide
Peroxide
A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen peroxide...
s. This affects the membrane permeability and results in the cell breakdown (lysis
Lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....
).
Although lactoferrin also has other antibacterial mechanisms not related to iron, such as stimulation of phagocytosis, the interaction with the outer bacterial membrane described above is the most dominant and most studied. Lactoferrin not only disrupts the membrane, but even penetrates into the cell. Its binding to the bacteria wall is associated with the specific peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
lactoferricin
Lactoferricin
Lactoferricin is an amphipathic, cationic peptide with anti-microbial and anti-cancer properties. It can be generated by the pepsin-mediated digestion of lactoferrin....
, which is located at the N-lobe of lactoferrin and is produced by in vitro cleavage of lactoferrin with another protein, trypsin
Trypsin
Trypsin is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when...
. A mechanism of the antimicrobial action of lactoferrin has been reported as lactoferrin targets H(+)-ATPase and interferes with proton translocation in the cell membrane, resulting in a lethal effect in vitro.
Antiviral activity
Lactoferrin acts, mostly in vitro, on a wide range of human and animal viruses based on DNA and RNA genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s, including the herpes simplex virus
Herpes simplex virus
Herpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
1 and 2, cytomegalovirus
Cytomegalovirus
Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...
, HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
, hepatitis C virus
Hepatitis C virus
Hepatitis C virus is a small , enveloped, positive-sense single-stranded RNA virus of the family Flaviviridae...
, hantavirus
Hantavirus
Hantaviruses are negative sense RNA viruses in the Bunyaviridae family. Humans may be infected with hantaviruses through rodent bites, urine, saliva or contact with rodent waste products...
es, rotavirus
Rotavirus
Rotavirus is the most common cause of severe diarrhoea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. It is a genus of double-stranded RNA virus in the family Reoviridae. By the age of five,...
es, poliovirus
Poliovirus
Poliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is...
type 1, human respiratory syncytial virus
Human respiratory syncytial virus
Human respiratory syncytial virus is a virus that causes respiratory tract infections. It is the major cause of lower respiratory tract infections and hospital visits during infancy and childhood. A prophylactic medication exists for preterm birth infants and infants with a congenital heart...
and murine leukemia virus
Murine leukemia virus
The murine leukemia viruses are retroviruses named for their ability to cause cancer in murine hosts. Some MLVs may infect other vertebrates. MLVs include both exogenous and endogenous viruses...
es.
The most studied mechanism of antiviral activity of lactoferrin is its diversion of virus particles from the target cells. Many viruses tend to bind to the lipoprotein
Lipoprotein
A lipoprotein is a biochemical assembly that contains both proteins and lipids water-bound to the proteins. Many enzymes, transporters, structural proteins, antigens, adhesins, and toxins are lipoproteins...
s of the cell membranes and then penetrate into the cell. Lactoferrin binds to the same lipoproteins thereby repelling the virus particles. Iron-free apolactoferrin is more efficient in this function than hololactoferrin; and lactoferricin, which is responsible for antimicrobial properties of lactoferrin, shows almost no antiviral activity.
Beside interacting with the cell walls, lactoferrin also directly binds to viral particles, such as the hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
viruses. This mechanism is also confirmed by the antiviral activity of lactoferrin against rotaviruses, which act on different cell types.
Lactoferrin also suppresses virus replication after the virus penetrated into the cell. Such an indirect antiviral effect is achieved by affecting natural killer cell
Natural killer cell
Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...
s, granulocyte
Granulocyte
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
s and macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
s – cells, which play a crucial role in the early stages of viral infections, such as severe acute respiratory syndrome
Severe acute respiratory syndrome
Severe Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...
(SARS).
Antifungal activity
Lactoferrin and lactoferricin inhibit in vitro growth of Trichophyton mentagrophytes, which are responsible for several skin diseases such as ringworm. Lactoferrin also acts against the Candida albicansCandida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...
– a diploid fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
(a form of yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
) that causes opportunistic
Opportunistic infection
An opportunistic infection is an infection caused by pathogens, particularly opportunistic pathogens—those that take advantage of certain situations—such as bacterial, viral, fungal or protozoan infections that usually do not cause disease in a healthy host, one with a healthy immune system...
oral and genital infections in humans. Fluconazole
Fluconazole
Fluconazole is a triazole antifungal drug used in the treatment and prevention of superficial and systemic fungal infections. In a bulk powder form, it appears as a white crystalline powder, and it is very slightly soluble in water and soluble in alcohol. It is commonly marketed under the trade...
has long been used against Candida albicans, which resulted in emergence of strains
Strain (biology)
In biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...
resistant to this drug. However, a combination of lactoferrin with fluconazole can act against fluconazole-resistant strains of Candida albicans as well as other types of Candida
Candida (genus)
Candida is a genus of yeasts. Many species are harmless commensals or endosymbionts of animal hosts including humans, but other species, or harmless species in the wrong location, can cause disease. Candida albicans can cause infections in humans and other animals, especially in immunocompromised...
: C. glabrata, C. krusei, C. parapsilosis and C. tropicalis. Antifungal activity is observed for sequential incubation of Candida with lactoferrin and then with fluconazole, but not vice versa. The antifungal activity of lactoferricin exceeds that of lactoferrin. In particular, synthetic peptide 1-11 lactoferricin shows much greater activity against Candida albicans than native lactoferricin.
Administration of lactoferrin through drinking water to mice with weakened immune systems and symptoms of aphthous ulcer
Aphthous ulcer
An aphthous ulcer , also known as a canker sore, is a type of mouth ulcer which presents as a painful open sore inside the mouth or upper throat characterized by a break in the mucous membrane. Its cause is unknown, but they are not contagious...
reduced the number of Candida albicans strains in the mouth and the size of the damaged areas in the tongue. Oral administration of lactoferrin to animals also reduced the number of pathogenic organisms in the tissues close to the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
. Candida albicans could also be completely eradicated with a mixture containing lactoferrin, lysozyme
Lysozyme
Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, are glycoside hydrolases, enzymes that damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between...
and introakonazol in HIV-positive patients who were resistant to other antifungal drugs. Such antifungal action when other drugs deem inefficient is characteristic of lactoferrin and is especially valuable for HIV-infected patients. Contrary to the antiviral and antibacterial actions of lactoferrin, very little is known about the mechanism of its antifungal action. Lactoferrin seems to destroy the cell wall and bind the plasma membrane of C. albicans.
Interaction with nucleic acids
One of the important properties of lactoferrin is its ability to bind with nucleic acids. The fraction of protein extracted from milk, contains 3.3% RNA,besides, the protein preferably binds to the double-stranded than to the single-stranded DNA. The ability of lactoferrin to bind DNA is used for the isolation and purification of lactoferrin using affinity chromatography
Affinity chromatography
Affinity chromatography is a method of separating biochemical mixtures and based on a highly specific interaction such as that between antigen and antibody, enzyme and substrate, or receptor and ligand.-Uses:Affinity chromatography can be used to:...
with columns containing immobilized DNA-containing sorbent
Sorbent
A sorbent is a material used to absorb liquids or gases. Examples include:*A material similar to molecular sieve material. It has a large internal surface area and good thermal conductivity. It is typically supplied in pellets of 1 mm to 2 mm diameter and roughly 5 mm length or as...
s, such as agarose with the immobilized single-stranded DNA.
Enzymatic activity of lactoferrin
Lactoferrin hydrolyzes RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and exhibits the properties of pyrimidine
Pyrimidine
Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...
-specific secretory ribonuclease
Ribonuclease
Ribonuclease is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within the EC 2.7 and 3.1 classes of enzymes.-Function:All organisms studied contain...
s. In particular, by destroying the RNA genome, milk RNase inhibits reverse transcription of retrovirus
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es that cause breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
in mice. Parsi
Parsi
Parsi or Parsee refers to a member of the larger of the two Zoroastrian communities in South Asia, the other being the Irani community....
women in West India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
have the milk RNase level markedly lower than in other groups, and their breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
rate is three times higher than average. Thus, ribonuclease
Ribonuclease
Ribonuclease is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within the EC 2.7 and 3.1 classes of enzymes.-Function:All organisms studied contain...
s of milk, and lactoferrin in particular, might play an important role in pathogenesis
Pathogenesis
The pathogenesis of a disease is the mechanism by which the disease is caused. The term can also be used to describe the origin and development of the disease and whether it is acute, chronic or recurrent...
of diseases caused by various retrovirus
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es.
Genes of lactoferrin
At least 60 gene sequences of lactoferrin have been characterized in 11 species of mammals. In most species, stop codonStop codon
In the genetic code, a stop codon is a nucleotide triplet within messenger RNA that signals a termination of translation. Proteins are based on polypeptides, which are unique sequences of amino acids. Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide...
is TAA, and TGA in Mus musculus. Deletions, insertions and mutations of stop codons affect the coding part and its length varies between 2,055 and 2,190 nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
pairs. Gene polymorphism between species is much more diverse than the intraspecific polymorphism of lactoferrin. There are differences in amino acid sequences: 8 in Homo sapiens, 6 in Mus musculus, 6 in Capra hircus, 10 in Bos taurus and 20 in Sus scrofa. This variation may indicate functional differences between different types of lactoferrin.
In humans, lactoferrin gene LTF is located on the third chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
in the locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
3q21-q23. In ox
Ox
An ox , also known as a bullock in Australia, New Zealand and India, is a bovine trained as a draft animal. Oxen are commonly castrated adult male cattle; castration makes the animals more tractable...
en, the coding sequence consists of 17 exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s and has a length of about 34,500 nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
pairs. Exons of the lactoferrin gene in oxen have a similar size to the exons of other genes of the transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...
family, whereas the sizes of introns differ within the family. Similarity in the size of exons and their distribution in the domains of the protein molecule indicates that the evolutionary development of lactoferrin gene occurred by duplication. Study of polymorphism of genes that encode lactoferrin helps selecting livestock breeds that are resistant to mastitis
Mastitis
Mastitis is the inflammation of breast tissue. S. aureus is the most common etiological organism responsible, but S. epidermidis and streptococci are occasionally isolated as well.-Terminology:...
.
Lactoferrin receptor
The lactoferrin receptorITLN1
Intelectin-1 also known as the intestinal lactoferrin receptor is a protein that in humans is encoded by the ITLN1 gene. Intelectin-1 functions both as a receptor for bacterial arabinogalactans and for lactoferrin.-Further reading:...
plays an important role in the internalization
Internalization
Internalization has different definitions depending on the field that the term is used in. Internalization is the opposite of externalization.- General :...
of lactoferrin; it also facilitates absorption of iron ions by lactoferrin. It was shown that gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
increases with age in the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
and decreases in the jejunum
Jejunum
The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
.
Cystic fibrosis
The human lung and saliva contain a wide range of antimicrobial compound including lactoperoxidase system, producing hypothiocyaniteHypothiocyanite
Hypothiocyanite is the anion [OSCN]- and the conjugate base of hypothiocyanous acid. It is an organic compound part of the thiocyanates as it contains the functional group SCN. It is formed when an oxygen is singly bonded to the thiocyanate group...
and lactoferrin, while hypothiocyanite is missing in cystic fibrosis
Cystic fibrosis
Cystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
patients. Lactoferrin, a component of innate immunity, prevents bacterial biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...
development. The loss of microbicidal activity and increased formation of biofilm due to decreased lactoferrin activity is observed in patients with cystic fibrosis. These findings demonstrate the important role of lactoferrin in human host defense and especially in lung.
Lactoferrin with hypothiocyanite has been granted orphan drug
Orphan drug
An orphan drug is a pharmaceutical agent that has been developed specifically to treat a rare medical condition, the condition itself being referred to as an orphan disease...
status by the EMEA
European Medicines Agency
The European Medicines Agency is a European agency for the evaluation of medicinal products. From 1995 to 2004, the European Medicines Agency was known as European Agency for the Evaluation of Medicinal Products.Roughly parallel to the U.S...
and the FDA.
Nanotechnology
Lactotransferrin has been used in the synthesis of fluorescent gold quantum clusters, which has potential applications in nanotechnology.External links
- Expasy Database, chemical structure
- LTF on the National Center for Biotechnology Information
- FDA Lactoferrin Considered Safe to Fight E. Coli.