Galectin
Encyclopedia
In molecular biology, galectins (also known as galaptins or S-lectin) are a family
of lectins which bind beta-galactoside
. The family is defined by having at least one characteristic carbohydrate
recognition domain (CRD) with an affinity for beta-galactosides and sharing certain sequence
elements. Members of the galectin family are found in mammals, birds, amphibians, fish
, nematodes, sponges, and some fungi
. Galectins are known to carry out intra
- and extracellular
functions, including inhibition of chronic inflammations, GVHD, and allergic reactions, through glycoconjugate-mediated recogntion. From the cytosol
they may be secreted by non-classical pathways, but they may also be targeted to the nucleus
or specific sub-cytosolic sites. Within the same peptide
chain some galectins have a CRD with only a few additional amino acids, whereas others have two CRDs joined by a link peptide, and one (galectin-3) has one CRD joined to a different type of domain.
Genes encoding galectin include:
(see also LGALS3
)
. The two sheets
are slightly bent with 6 strands forming the concave side and 5 strands forming the convex side. The concave side forms a groove in which carbohydrate
is bound, and which is long enough to hold about a linear tetrasaccharide
.
Protein family
A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....
of lectins which bind beta-galactoside
Beta-galactoside
A β-galactoside is a type of galactoside in which the glycosidic bond lies above the plane of the galactose residue. The most commonly recognized and used β-galactoside in biochemistry is Lactose. However, other chemicals, such as ONPG, are known, but these are typically synthesized for...
. The family is defined by having at least one characteristic carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
recognition domain (CRD) with an affinity for beta-galactosides and sharing certain sequence
Sequence (biology)
A sequence in biology is the one-dimensional ordering of monomers, covalently linked within in a biopolymer; it is also referred to as the primary structure of the biological macromolecule.-See also:* Protein sequence* DNA sequence...
elements. Members of the galectin family are found in mammals, birds, amphibians, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, nematodes, sponges, and some fungi
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...
. Galectins are known to carry out intra
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...
- and extracellular
Extracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...
functions, including inhibition of chronic inflammations, GVHD, and allergic reactions, through glycoconjugate-mediated recogntion. From the cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
they may be secreted by non-classical pathways, but they may also be targeted to the nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
or specific sub-cytosolic sites. Within the same 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...
chain some galectins have a CRD with only a few additional amino acids, whereas others have two CRDs joined by a link peptide, and one (galectin-3) has one CRD joined to a different type of domain.
Genes encoding galectin include:
(see also LGALS3
LGALS3
Galectin-3 is a protein that in humans is encoded by the LGALS3 gene. In melanocytic cells LGALS3 gene expression may be regulated by MITF.-Interactions:LGALS3 has been shown to interact with LGALS3BP.-Further reading:...
)
Structure
The galectin carbohydrate recognition domain (CRD) is a beta-sandwich of about 135 amino acidAmino 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...
. The two sheets
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...
are slightly bent with 6 strands forming the concave side and 5 strands forming the convex side. The concave side forms a groove in which carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
is bound, and which is long enough to hold about a linear tetrasaccharide
Tetrasaccharide
A tetrasaccharide is a carbohydrate which gives upon hydrolysis four molecules of the same or different monosaccharides. For example, stachyose upon hydrolysis gives one molecule each of glucose and fructose and two molecules of galactose. The general formula of a tetrasaccharide is typically...
.