1wgc

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spinqualitylabelsall models 1wgc, resolution 2.2Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

2.2 ANGSTROMS RESOLUTION STRUCTURE ANALYSIS OF TWO REFINED N-ACETYLNEURAMINYLLACTOSE-WHEAT GERM AGGLUTININ ISOLECTIN COMPLEXES

Overview

The crystal structures of complexes of isolectins 1 and 2 of wheat germ, agglutinin (WGA1 and WGA2) with N-acetylneuraminyl-lactose, (NeuNAc-alpha(2-3)-Gal-beta(1-4)-Glc) have been refined on the basis of, data in the 8 to 2.2 A resolution range to final crystallographic, R-factors of 17.2% and 15.3% (Fo greater than 1 sigma), respectively., Specific binding interactions and water association, as well as changes in, conformation and mobility of the structure upon ligand binding, were, compared in the two complexes. The temperature factors (B = 16.3 A2 and, 18.4 A2) were found to be much lower compared with those of their, respective native structures (19 to 22 A2). Residues involved in sugar, binding, dimerization and in lattice contacts exhibit the largest, decreases in B-value, suggesting that sugar binding reduces the overall, mobility of the protein molecules in the crystal lattice. The binding mode, of this sialyl-trisaccharide, an important cell receptor analogue, has, been compared in the two isolectins. Only one of the two unique binding, sites (4 per dimer), located in the subunit/subunit interface, is occupied, in the crystals. This site, termed the "primary" binding site, contains, one of the five amino acid substitutions that differentiate WGA1 and WGA2., Superposition of the refined models in each of the independent, crystallographic environments indicates a close match only of the terminal, non-reducing NeuNAc residue (root-mean-square delta r of 0.5 to 0.6 A)., The Gal-Glc portion was found to superimpose poorly, lack electron, density, and possess high atomic thermal factors. In both complexes NeuNAc, is stabilized through contact with six amino acid side-chains (Ser114 and, Glu115 of subunit 1 and Ser62, Tyr64, Tyr(His)66 and Tyr73 of subunit 2), involving all NeuNAc ring substituents. Refinement has allowed accurate, assessment of the contact distances for four hydrogen bonds, a strong, buried non-polar contact with the acetamido CH3 group and a large number, of van der Waals' interactions with the three aromatic side-chains. The, higher affinity of N-acetylneuraminyl-lactose observed by nuclear magnetic, resonance studies for WGA1 can be explained by the more favorable binding, interactions that occur when residue 66 is a Tyr. The tyrosyl side-chain, provides a larger surface for van der Waals' stacking against the NeuNAc, pyranose ring than His66 and a hydrogen bond contact with Gal (C2-OH), not, possible in WGA2.(ABSTRACT TRUNCATED AT 400 WORDS)

About this Structure

1WGC is a Single protein structure of sequence from [1]. Full crystallographic information is available from OCA.

Reference

2.2 A resolution structure analysis of two refined N-acetylneuraminyl-lactose--wheat germ agglutinin isolectin complexes., Wright CS, J Mol Biol. 1990 Oct 20;215(4):635-51. PMID:2231724

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