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Glycobiology Advance Access published online on July 8, 2003
Glycobiology, doi:10.1093/glycob/cwg095
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Submitted on May 12, 2003
Accepted on June 19, 2003

© 2003 Oxford University Press

ORIGINAL ARTICLES

Computational analysis of multivalency in lectins: structures of garlic lectin-oligosachharide complexes and their aggregates

Gosu Ramachandraiah 1, Nagasuma R. Chandra 2, A. Surolia 1, and M. Vijayan 1*

1 Molecular Biophysics Unit, Indian Institute of Science, Bangalore, INDIA 560012
2 Bioinformatics Centre, Indian Institute of Science, Bangalore, INDIA 560012

* To whom correspondence should be addressed. E-mail: mv{at}mbu.iisc.ernet.in.

Abstract

Multivalency in lectins is a phenomenon, which has been discussed at considerable length. The structural basis for the role of multivalency in garlic lectin has been investigated here through computational studies. Biochemical studies have shown that the binding affinity of garlic lectin for high mannose oligosaccharides is orders of magnitude greater than that for mannose. Modeling and energy calculations clearly indicate that such increase in affinity cannot be accounted for, by binding of these oligosaccharides at any of the six sites of a garlic lectin dimer. These studies also indicate that a given oligosaccharide cannot bind simultaneously to more than one binding site on a lectin dimer. The possibility of a given oligosaccharide simultaneously binding to, and hence linking two or more lectin molecules was therefore explored. This study showed that trimannosides and higher oligomers can crosslink lectin dimers, amplifying the protein-oligosaccharide interactions several-fold, thus explaining the role of multivalency in enhancing affinity. A comprehensive exploration of all possible crosslinks, posed a formidable computational problem. Even a partial exploration involving a carefully chosen region of the conformational space, clearly showed that a given dimer-pair can be crosslinked not only by a single oligosaccharide molecule, but also simultaneously by two oligosaccharides. The number of such possible ‘double-crosslinks', including those forming interesting tetrameric structures, generally increases with the size of the oligosachharide, correlating with the biochemical data. In addition to their immediate relevance to garlic lectin, these studies are of general interest in relation to lectin-oligosaccharide interactions.


affinity enhancement, cross-linking, multiple binding sites, oligosachharide binding
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