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Evaluation of the stoichiometry and energetics of carbohydrate binding to Ricinus communis agglutinin: a calorimetric study

Sharma, Shalini and Bharadwaj, Satish and Surolia, Avadhesha and Podder, Sunil Kumar (1998) Evaluation of the stoichiometry and energetics of carbohydrate binding to Ricinus communis agglutinin: a calorimetric study. In: Biochemical Journal, 333 (3). pp. 539-542.


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High-sensitivity isothermal titration calorimetry has been used to investigate the thermodynamics of binding of Ricinus communis agglutinin to galactose, lactose and their derivatives in the temperature range 280.5-298 K. The present study unequivocally establishes the carbohydrate-binding stoichiometry of the tetrameric agglutinin from castor bean as two, i.e. the (As-sB)(2)-type tetramer of the agglutinin has two equivalent sites that are noninteracting and independent. The site binding constants range from 2.2 x 10(3) M-1 at 282 K for galactose to 4.84 x 10(4) M-1 at 281 K for N-acetyl- lactosamine. The binding enthalpies range from -21.9 kJ.mol(-1) at 293 K for 4-methylumbelliferyl-beta-galactoside to -50.2 kJ.mol(-1) at 292.9 K for thiodigalactoside. The observation of limited entropy-enthalpy compensation for binding of the sugars to the lectin indicates that reorganization of water molecules plays an important role in binding. As the slope of the compensation plot is greater than unity, the reactions are largely enthalpically driven. These studies show that the stronger binding of N-acetyl-lactosamine than lactose is due to a favourable interaction between the acetamido group of the reducing-end N-acetylglucosamine of the former and the corresponding loci in the agglutinin molecule. Preferential binding of methyl-beta-galactoside over methyl-alpha- galactoside also indicates the apolar nature of the interaction with the methyl group of the former sugar.

Item Type: Journal Article
Publication: Biochemical Journal
Publisher: Portland Press
Additional Information: Mounted on the Internet with permission from Portland Press (1998).
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Biological Sciences > Biochemistry
Date Deposited: 22 Sep 2004
Last Modified: 19 Sep 2010 04:15
URI: http://eprints.iisc.ac.in/id/eprint/1416

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