1byf

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STRUCTURE OF TC14; A C-TYPE LECTIN FROM THE TUNICATE POLYANDROCARPA MISAKIENSIS

Overview

C-type lectins are calcium-dependent carbohydrate-recognising proteins., Isothermal titration calorimetry of the C-type Polyandrocarpa lectin, (TC14) from the tunicate Polyandrocarpa misakiensis revealed the presence, of a single calcium atom per monomer with a dissociation constant of 2.6, microM, and confirmed the specificity of TC14 for D -galactose and related, monosaccharides. We have determined the 2.2 A X-ray crystal structure of, Polyandrocarpa lectin complexed with D -galactose. Analytical, ultracentrifugation revealed that TC14 behaves as a dimer in solution., This is reflected by the presence of two molecules in the asymmetric unit, with the dimeric interface formed by antiparallel pairing of the two, N-terminal beta-strands and hydrophobic interactions. TC14 adopts a, typical C-type lectin fold with differences in structure from other C-type, lectins mainly in the diverse loop regions and in the second alpha-helix, which is involved in the formation of the dimeric interface. The D, -galactose is bound through coordination of the 3 and 4-hydroxyl oxygen, atoms with a bound calcium atom. Additional hydrogen bonds are formed, directly between serine, aspartate and glutamate side-chains of the, protein and the sugar 3 and 4-hydroxyl groups. Comparison of the galactose, binding by TC14 with the mannose binding by rat mannose-binding protein, reveals how monosaccharide specificity is achieved in this lectin. A, tryptophan side-chain close to the binding site and the distribution of, hydrogen-bond acceptors and donors around the 3 and 4-hydroxyl groups of, the sugar are essential determinants of specificity. These elements are, however, arranged in a very different way than in an engineered, galactose-specific mutant of MBPA. Possible biological functions can more, easily be understood from the fact that TC14 is a dimer under, physiological conditions.

About this Structure

1BYF is a Single protein structure of sequence from Polyandrocarpa misakiensis with , , and as ligands. Known structural/functional Sites: and . Full crystallographic information is available from OCA.

Reference

The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose., Poget SF, Legge GB, Proctor MR, Butler PJ, Bycroft M, Williams RL, J Mol Biol. 1999 Jul 23;290(4):867-79. PMID:10398588

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