legume lectins, lectin-like receptor kinases, arcelin, concanavalinA, and alpha-amylase inhibitor
This alignment model includes the legume lectins (also known as agglutinins), the arcelin (also known as phytohemagglutinin-L) family of lectin-like defense proteins, the LecRK family of lectin-like receptor kinases, concanavalinA (ConA), and an alpha-amylase inhibitor. Arcelin is a major seed glycoprotein discovered in kidney beans (Phaseolus vulgaris) that has insecticidal properties and protects the seeds from predation by larvae of various bruchids. Arcelin is devoid of monosaccharide binding properties and lacks a key metal-binding loop that is present in other members of this family. Phytohaemagglutinin (PHA) is a lectin found in plants, especially beans, that affects cell metabolism by inducing mitosis and by altering the permeability of the cell membrane to various proteins. PHA agglutinates most mammalian red blood cell types by binding glycans on the cell surface. Medically, PHA is used as a mitogen to trigger cell division in T-lymphocytes and to activate latent HIV-1 from human peripheral lymphocytes. Plant L-type lectins are primarily found in the seeds of leguminous plants where they constitute about 10% of the total soluble protein of the seed extracts. They are synthesized during seed development several weeks after flowering and transported to the vacuole where they become condensed into specialized vesicles called protein bodies. L-type lectins have a dome-shaped beta-barrel carbohydrate recognition domain with a curved seven-stranded beta-sheet referred to as the "front face" and a flat six-stranded beta-sheet referred to as the "back face". This domain homodimerizes so that adjacent back sheets form a contiguous 12-stranded sheet and homotetramers occur by a back-to-back association of these homodimers. Though L-type lectins exhibit both sequence and structural similarity to one another, their carbohydrate binding specificities differ widely.