Journal of Biological Chemistry
Volume 274, Issue 42, 15 October 1999, Pages 29694-29698
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CARBOHYDRATES, LIPIDS, AND OTHER NATURAL PRODUCTS
Thermodynamic Studies of Saccharide Binding to Artocarpin, a B-Cell Mitogen, Reveals the Extended Nature of Its Interaction with Mannotriose [3,6-Di-O-(α-d-mannopyranosyl)-d-mannose]*

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The thermodynamics of binding of various saccharides to artocarpin, from Artocarpus integrifoliaseeds, a homotetrameric lectin (M r 65,000) with one binding site per subunit, was determined by isothermal titration calorimetry measurements at 280 and 293 K. The binding enthalpies, ΔHb, are the same at both temperatures, and the values range from −10.94 to −47.11 kJ mol−1. The affinities of artocarpin as obtained from isothermal titration calorimetry are in reasonable agreement with the results obtained by enzyme-linked lectin absorbent essay, which is based on the minimum amount of ligand required to inhibit horseradish peroxidase binding to artocarpin in enzyme-linked lectin absorbent essay (Misquith, S., Rani, P. G., and Surolia, A. (1994) J. Biol. Chem. 269, 30393–30401). The interactions are mainly enthalpically driven and exhibit enthalpy-entropy compensation. The order of binding affinity of artocarpin is as follows: mannotriose>Manα3Man>GlcNAc2Man3>MeαMan>Man>Manα6Man>Manα2Man>MeαGlc>Glc,i.e. 7>4>2>1.4>1>0.4>0.3>0.24>0.11. The ΔH for the interaction of Manα3Man, Manα6Man, and MeαMan are similar and 20 kJ mol−1 lower than that of mannotriose. This indicates that, while Manα3Man and Manα6Man interact with the lectin exclusively through their nonreducing end monosaccharide with the subsites specific for the α1,3 and α1,6 arms, the mannotriose interacts with the lectin simultaneously through all three of its mannopyranosyl residues. This study thus underscores the distinction in the recognition of this common oligosaccharide motif in comparison with that displayed by other lectins with related specificity.

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This work was supported by the Department of Science & Technology, and the OMEGA titration calorimeter was provided by a grant from the Department of Biotechnology, Government of India (to A. S.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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