The Man/Glc-specific seed lectin from Dioclea grandiflora (DGL) is a member of the Diocleinae subtribe that includes the jack bean lectin Con A (ConA). Both DGL and ConA bind with high affinity to the \"core\" trimannoside moiety, 3,6-di-O-(a-D-mannopyranosyl)-a-D-mannopyranoside, which is present in asparagine-linked carbohydrates. Recent hemagglutination inhibition studies suggest that DGL and ConA recognize similar epitopes of the trisaccharide but possess different binding specificities for complex carbohydrates (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 titrn. microcalorimetry to det. the thermodn. of binding of DGL to a complete set of monodeoxy analogs of the core trimannoside as well as a tetradeoxy analog. The thermodn. data indicate that DGL recognizes the 2-, 3-, 4-, and 6-hydroxyl groups of the a(1,6) Man residue, the 3- and 4-hydroxyl group of the a(1,3) Man residue, and the 2- and 4-hydroxyl groups of the central Man residue of the trimannoside. The thermodn. data for the tetradeoxy analog lacking the 3- and 4-hydroxyl group of the a(1,3) Man residue, and the 2- and 4-hydroxyl groups of the central Man residue of the trimannoside are consistent with the involvement of these hydroxyl groups in binding. While the overall 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 monodeoxy analogs binding to the two lectins. Differences are also obsd. in the thermodn. of binding of DGL and ConA to a biantennary complex carbohydrate. In the following paper (Rozwarski, D. A., Swami, B. M., Brewer, C. F., and Sacchettini, J. C. (1988) J. Biol. Chem. 273, 32818-32825), the x-ray crystal structure of DGL complexed to the core trimannoside is presented, and a comparison is made of the thermodn. binding data for DGL and ConA as well as the structure of their resp. trimannoside complexes. [on SciFinder (R)]