Structure and sugar-specificity of basic winged-bean lectin: structures of new disaccharide complexes and a comparative study with other known disaccharide complexes of the lectin

Kulkarni, Kiran A and Katiyar, Samiksha and Surolia, Avadhesha and Vijayan, Mamannamana and Suguna, Kaza (2008) Structure and sugar-specificity of basic winged-bean lectin: structures of new disaccharide complexes and a comparative study with other known disaccharide complexes of the lectin. In: Acta Crystallographica Section D: Biological Crystallography, 64 (7). pp. 730-737.

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Abstract

Crystal structures of the complexes of basic winged-bean agglutinin with the disaccharides Gal \alpha1-4Gal (galabiose), Gal \alpha1-6Glc (mellibiose) and Gal \alpha1-4Gal \beta-Et have been determined and the complex with Gal\alpha1-2Gal has been modelled. The interactions of the nonreducing Gal with the lectin at the primary site are the same as those in the known complexes with disaccharides having the $\alpha 1 \rightarrow 3$ linkage. The second residue in Gal \alpha1-4Gal and Gal \alpha1-6Glc forms a water bridge to the lectin, while the ethyl group in Gal \alpha1-4Gal \beta-Et makes nonpolar interactions. In complexes involving disaccharides with \alpha1-3 linkages, which form part of the A and B blood-group substances, the second sugar residue forms a direct hydrogen bond to the variable loop in the binding site of the lectin. This in part explains the specificity of the lectin for the blood-group substances and also the higher affinity of $\alpha 1 \rightarrow 3$-linked disaccharides for the lectin compared with disaccharides involving other linkages. Including those reported here, 14 crystal structures involving the lectin, accounting for 54 crystallographically independent subunits, are available. A comparative study of these structures shows that the region involving the curved \beta-sheet which nestles the metal ions is relatively rigid. The carbohydrate-binding region is perched on this region. The flat \beta-sheet, which is involved in oligomerization and exhibits considerable variability in legume lectins, is relatively flexible. Indeed, the structures of basic winged-bean lectin have been of critical importance in establishing legume lectins as a family of proteins in which small alterations in essentially the same tertiary structure lead to large variations in quaternary association. They have also provided a structural explanation of the blood-group specificity of the lectin.

Item Type:	Journal Article
Publication:	Acta Crystallographica Section D: Biological Crystallography
Publisher:	International Union of Crystallography
Additional Information:	Copyright of this article belongs to International Union of Crystallography.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	18 Jul 2008
Last Modified:	19 Sep 2010 04:47
URI:	http://eprints.iisc.ac.in/id/eprint/15104

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