Legume lectin

[2][3] The exact function of the legume lectins in vivo is unknown but they are probably involved in the defense of plants against predators.

They have been used for decades as a model system for the study of protein-carbohydrate interactions, because they show a wide variety of binding specificities and are easy to obtain, purify, and characterize the structure of.

[3] Well-studied members of this protein family include phytohemagglutinin, soybean agglutinins, and concanavalin A.

The legume lectins use an ingenious framework for binding specific sugars.

This framework consists of a conserved monosaccharide binding site in which four conserved residues from four separate regions in the protein confer affinity (see figure), a variable loop that confers monosaccharide specificity and a number of subsites around the monosaccharide binding site that harbour additional sugar residues or hydrophobic groups.

A typical legume lectin monomer ( lentil lectin), complexed with a sugar ( glucose ). The four sugar-binding loops are shown in different colours. The variable loop that confers monosaccharide specificity is shown in orange.
Quaternary structures of some legume lectins. One of the subunits is in the same orientation in all structures for ease of comparison.