Kunitz domain
Encyclopedia
Kunitz domains are the active domains
of protein
s that inhibit the function of protein degrading enzymes
or, more specifically, domains of Kunitz-type protease inhibitors
. They are relatively small with a length of about 50 to 60 amino acid
s and a molecular weight of 6 kDa
. Examples of Kunitz-type protease inhibitors are aprotinin
(bovine pancreatic trypsin inhibitor, BPTI), Alzheimer's amyloid precursor protein
(APP), and tissue factor pathway inhibitor
(TFPI).
Standalone Kunitz domains are used as a framework for the development of new pharmaceutical drugs.
rich alpha+beta fold. Bovine pancreatic trypsin inhibitor is an extensively studied model structure. Certain family members are similar to the tick
anticoagulant peptide (TAP). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways. TAP molecules are highly dipolar, and are arranged to form a twisted two-stranded antiparallel beta sheet
followed by an alpha helix
.
The majority of the sequences having this domain belong to the MEROPS
inhibitor family I2, clan IB; the Kunitz/bovine pancreatic trypsin inhibitor family, they inhibit proteases of the S1 family and are restricted to the metazoa with a single exception: Amsacta moorei entomopoxvirus, a species of poxvirus. They are short (about 50 to 60 amino acid residues) alpha/beta proteins with few secondary structures. The fold is constrained by three disulfide bonds. The type example for this family is BPTI (or basic protease inhibitor), but the family includes numerous other members, such as snake venom basic protease; mammalian inter-alpha-trypsin inhibitor
s; trypstatin, a rat mast cell inhibitor of trypsin; a domain found in an alternatively spliced form of Alzheimer's amyloid beta-protein; domains at the C-termini of the alpha-1
and alpha-3 chains
of type VI and type VII collagen
s; tissue factor pathway inhibitor precursor; and Kunitz STI protease inhibitor
contained in legume seeds.
s, able to recognise specific protein structures, and also work as competitive
protease inhibitors in their free form. These properties have led to attempts at developing biopharmaceutical
drugs from Kunitz domains. Candidate domains are selected from molecular libraries containing over 10 million variants with the aid of display techniques like phage display
, and can be produced in large scale by genetically engineered organisms.
The first of these drugs to be marketed was the kallikrein
inhibitor ecallantide
, used for the treatment of hereditary angioedema
. It was approved in the United States in 2009. Another example is depelestat, an inhibitor of neutrophil elastase that has undergone Phase II clinical trial
s for the treatment of acute respiratory distress syndrome
in 2006/2007 and has also been described as a potential inhalable cystic fibrosis
treatment.
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...
of protein
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...
s that inhibit the function of protein degrading enzymes
Protease
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....
or, more specifically, domains of Kunitz-type protease inhibitors
Protease inhibitor (biology)
In biology and biochemistry, protease inhibitors are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins....
. They are relatively small with a length of about 50 to 60 amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s and a molecular weight of 6 kDa
KDA
KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...
. Examples of Kunitz-type protease inhibitors are aprotinin
Aprotinin
The drug aprotinin , is the bovine version of the small protein basic pancreatic trypsin inhibitor, or BPTI, which inhibits trypsin and related proteolytic enzymes. Under the trade name Trasylol, aprotinin was used as a medication administered by injection to reduce bleeding during complex surgery,...
(bovine pancreatic trypsin inhibitor, BPTI), Alzheimer's amyloid precursor protein
Amyloid precursor protein
Amyloid precursor protein is an integral membrane protein expressed in many tissues and concentrated in the synapses of neurons. Its primary function is not known, though it has been implicated as a regulator of synapse formation, neural plasticity and iron export...
(APP), and tissue factor pathway inhibitor
Tissue factor pathway inhibitor
Tissue factor pathway inhibitor is a single-chain polypeptide which can reversibly inhibit Factor Xa and Thrombin...
(TFPI).
Standalone Kunitz domains are used as a framework for the development of new pharmaceutical drugs.
Structure
The structure is a disulfideDisulfide
In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. Disulfide usually refer to a chemical compound that contains a disulfide bond, such as diphenyl disulfide, C6H5S-SC6H5....
rich alpha+beta fold. Bovine pancreatic trypsin inhibitor is an extensively studied model structure. Certain family members are similar to the tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
anticoagulant peptide (TAP). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways. TAP molecules are highly dipolar, and are arranged to form a twisted two-stranded antiparallel beta sheet
Beta sheet
The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...
followed by an alpha helix
Alpha helix
A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
.
The majority of the sequences having this domain belong to the MEROPS
Merops
Merops may refer to:* Merops , a genus of bee-eaters.* MEROPS, an on-line database for peptidases.It may also refer to several figures from Greek mythology:* King of Ethiopia, husband of Clymene, who lay with Helios and bore Phaethon...
inhibitor family I2, clan IB; the Kunitz/bovine pancreatic trypsin inhibitor family, they inhibit proteases of the S1 family and are restricted to the metazoa with a single exception: Amsacta moorei entomopoxvirus, a species of poxvirus. They are short (about 50 to 60 amino acid residues) alpha/beta proteins with few secondary structures. The fold is constrained by three disulfide bonds. The type example for this family is BPTI (or basic protease inhibitor), but the family includes numerous other members, such as snake venom basic protease; mammalian inter-alpha-trypsin inhibitor
Inter-alpha-trypsin inhibitor
Inter-alpha-trypsin inhibitors are plasma proteins consisting of three of four heavy chains selected from the group ITIH1, ITIH2, ITIH3, ITIH4 and one light chain selected from the group AMBP or SPINT2. They function as protease inhibitors....
s; trypstatin, a rat mast cell inhibitor of trypsin; a domain found in an alternatively spliced form of Alzheimer's amyloid beta-protein; domains at the C-termini of the alpha-1
COL6A1
Collagen alpha-1 chain is a protein that in humans is encoded by the COL6A1 gene.- Function :The collagens are a superfamily of proteins that play a role in maintaining the integrity of various tissues. Collagens are extracellular matrix proteins and have a triple-helical domain as their common...
and alpha-3 chains
COL6A3
Collagen alpha-3 chain is a protein that in humans is encoded by the COL6A3 gene.- Function :This gene encodes the alpha 3 chain, one of the three alpha chains of type VI collagen, a beaded filament collagen found in most connective tissues. The alpha 3 chain of type VI collagen is much larger than...
of type VI and type VII collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
s; tissue factor pathway inhibitor precursor; and Kunitz STI protease inhibitor
Kunitz STI protease inhibitor
Kunitz STI protease inhibitor is a type of protein contained in legume seeds which functions as a protease inhibitor. Kunitz-type Soybean Trypsin Inhibitors are usually specific for either trypsin or chymotrypsin...
contained in legume seeds.
Drug development
Kunitz domains are stable as standalone peptidePeptide
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...
s, able to recognise specific protein structures, and also work as competitive
Competitive inhibition
Competitive inhibition is a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa.-Mechanism:...
protease inhibitors in their free form. These properties have led to attempts at developing biopharmaceutical
Biopharmaceutical
Biopharmaceuticals are medical drugs produced using biotechnology. They include proteins , nucleic acids and living microorganisms like virus and bacteria where the virulence of viruses and bacteria is reduced by the process of attenuation, they can be used for therapeutic or in vivo diagnostic...
drugs from Kunitz domains. Candidate domains are selected from molecular libraries containing over 10 million variants with the aid of display techniques like phage display
Phage display
Phage display is a method for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. Phage Display was originally invented by George P...
, and can be produced in large scale by genetically engineered organisms.
The first of these drugs to be marketed was the kallikrein
Kallikrein
Kallikreins are a subgroup of serine proteases, enzymes capable of cleaving peptide bonds in proteins. In humans, plasma kallikrein has no known homologue, while tissue kallikrein-related peptidases encode a family of fifteen closely related serine proteases...
inhibitor ecallantide
Ecallantide
Ecallantide is a drug used for the treatment of hereditary angioedema and in the prevention of blood loss in cardiothoracic surgery. It is an inhibitor of the protein kallikrein and a 60-amino acid polypeptide which was developed from a Kunitz domain through phage display to mimic antibodies...
, used for the treatment of hereditary angioedema
Angioedema
Angioedema or Quincke's edema is the rapid swelling of the dermis, subcutaneous tissue, mucosa and submucosal tissues. It is very similar to urticaria, but urticaria, commonly known as hives, occurs in the upper dermis...
. It was approved in the United States in 2009. Another example is depelestat, an inhibitor of neutrophil elastase that has undergone Phase II clinical trial
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...
s for the treatment of acute respiratory distress syndrome
Acute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
in 2006/2007 and has also been described as a potential inhalable cystic fibrosis
Cystic fibrosis
Cystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
treatment.
Examples
Human proteins containing this domain include:- AMBP, APLP2APLP2Amyloid beta precursor-like protein 2, also known as APLP2, is a protein that in humans is encoded by the APLP2 gene. APLP2 along with APLP1 are important modulators of glucose and insulin homeostasis.- Function :...
, APPAmyloid precursor proteinAmyloid precursor protein is an integral membrane protein expressed in many tissues and concentrated in the synapses of neurons. Its primary function is not known, though it has been implicated as a regulator of synapse formation, neural plasticity and iron export... - COL6A3COL6A3Collagen alpha-3 chain is a protein that in humans is encoded by the COL6A3 gene.- Function :This gene encodes the alpha 3 chain, one of the three alpha chains of type VI collagen, a beaded filament collagen found in most connective tissues. The alpha 3 chain of type VI collagen is much larger than...
, COL7A1, COL28A1COL28A1Collagen, type XXVIII, alpha 1 also known as COL28A1 is a protein that in humans is encoded by the COL28A1 gene. The protein encoded by this gene is a collagen.... - PAPLNPAPLNPapilin is a protein that in humans is encoded by the PAPLN gene. Papilin is an extracellular matrix glycoprotein....
, - SPINLW1SPINLW1Eppin is a protein that in humans is encoded by the SPINLW1 gene.-Further reading:...
, SPINT1SPINT1Kunitz-type protease inhibitor 1 is an enzyme that in humans is encoded by the SPINT1 gene.-Further reading:...
, SPINT2SPINT2Kunitz-type protease inhibitor 2 is an enzyme that in humans is encoded by the SPINT2 gene.-Further reading:...
, SPINT3, SPINT4 - TFPITissue factor pathway inhibitorTissue factor pathway inhibitor is a single-chain polypeptide which can reversibly inhibit Factor Xa and Thrombin...
, TFPI2TFPI2Tissue factor pathway inhibitor 2 is a protein that in humans is encoded by the TFPI2 gene.-Further reading:... - WFDC6, WFDC8, WFIKKN1WFIKKN1WAP, kazal, immunoglobulin, kunitz and NTR domain-containing protein 1 is a protein that in humans is encoded by the WFIKKN1 gene.-Further reading:...
, WFIKKN2