Crystal Structures of the Peanut Lectin-Lactose Complex at Acidic pH: Retention of Unusual Quaternary Structure, Empty and Carbohydrate Bound Combining Sites, Molecular Mimicry and Crystal Packing Directed by Interactions at the Combining Site

Ravishankar, R and Thomas, CJ and Suguna, K and Surolia, A and Vijayan, M (2001) Crystal Structures of the Peanut Lectin-Lactose Complex at Acidic pH: Retention of Unusual Quaternary Structure, Empty and Carbohydrate Bound Combining Sites, Molecular Mimicry and Crystal Packing Directed by Interactions at the Combining Site. In: Proteins: Structure, Function, and Genetics, 43 (3). pp. 260-270.

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Abstract

The crystal structures of a monoclinic and a triclinic form of the peanut lectin-lactose complex, grown at pH 4.6, have been determined. They contain two and one crystallographically independent tetramers, respectively. The unusual "open" quaternary structure of the lectin, observed in the orthorhombic complex grown in neutral pH, is retained at the acidic pH. The sugar molecule is bound to three of the eight subunits in the monoclinic crystals, whereas the combining sites in four are empty. The lectin-sugar interactions are almost the same at neutral and acidic pH. A comparison of the sugar-bound and free subunits indicates that the geometry of the combining site is relatively unaffected by ligand binding. The combining site of the eighth subunit in the monoclinic crystals is bound to a peptide stretch in a loop from a neighboring molecule. The same interaction exists in two subunits of the triclinic crystals, whereas density corresponding to sugar exists in the combining sites of the other two subunits. Solution studies show that oligopeptides with sequences corresponding to that in the loop bind to the lectin at acidic pH, but only with reduced affinity at neutral pH. The reverse is the case with the binding of lactose to the lectin. A comparison of the neutral and acidic pH crystal structures indicates that the molecular packing in the latter is directed to a substantial extent by the increased affinity of the peptide loop to the combining site at acidic pH. Proteins 2001;43:260-270.

Item Type:	Journal Article
Publication:	Proteins: Structure, Function, and Genetics
Publisher:	Wiley-Liss, Inc
Additional Information:	The copyright belongs to Wiley-Liss, Inc.
Keywords:	Lectins;Quaternary association;Carbohydrate specificity; Molecular mimicry;Ligand binding;Molecular packing
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	28 Mar 2006
Last Modified:	19 Sep 2010 04:24
URI:	http://eprints.iisc.ac.in/id/eprint/5614

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