Thermodynamics of binding of the core trimannoside of asparagine-linked carbohydrates and deoxy analogs to Dioclea grandiflora lectin

The Man/Glc-specific seed lectin from Dioclea grandiflora (DGL) is a member of the Diocleinae subtribe that includes the jack bean lectin concanavalin A (ConA). Both DGL and ConA bind with high affinity to the "core" trimanno side moiety, 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, whi ch is present in asparagine-linked carbohydrates. Recent hemagglutination i nhibition studies suggest that DGL and ConA recognize similar epitopes of t he trisaccharide but possess different binding specificities for complex ca rbohydrates (Gupta, D., Oscarson, S., Raju, T. S., Stanley, P., Toone, E. J ., and Brewer, C. F. (1996) Eur. J. Biochem. 242, 320-326). In the present study, we have used isothermal titration microcalorimetry to determine the thermodynamics of binding of DGL to a complete set of monodeoxy analogs of the core trimannoside as web as a tetradeoxy analog. The thermodynamic data indicate that DGL recognizes the 2-, 3-, 4-, and 6-hydroxyl groups of the alpha(1,6) Man residue, the 3- and 4-hydroxyl group of the alpha(1, 3) Man residue, and the 2- and 4-hydroxyl groups of the central Man residue of the trimannoside. The thermodynamic data for the tetradeoxy analog lacking the 3- and I-hydroxyl group of the alpha(1, 3) Man residue, and the 2- and 4-h ydroxyl groups of the central Man residue of the trimannoside are consisten t with the involvement of these hydroxyl groups in binding. While the overa ll pattern of data for DGL binding to the deoxy analogs is similar to that for ConA (Gupta, D., Dam, T. K., Oscarson, S., and Brewer, C. F. (1997) J. Biol. Chem. 272, 6388-6392), differences exist in the data for certain mono deoxy analogs binding to the two lectins. Differences are also observed in the thermodynamics of binding of DGL and ConA to a biantennary complex carb ohydrate. In the following paper (Rozwarski, D. A., Swami, B. M., Brewer, C . F., and Sacchettini, J. C. (1998) J. Biol. Chem. 273, 32818-32825), the x -ray crystal structure of DGL complexed to the core trimannoside is present ed, and a comparison is made of the thermodynamic binding data for DGL and ConA as well as the structures of their respective trimannoside complexes.