Thermodynamic studies of the binding of "core" trimannos1de and deoxy analogs to concanavalin a and dioclea grandiflora lectin

The core trimannoside of all asparagine-linked carbohydrates, 3,6-di-O_- ( ctD-mannopyranosyl)-D-mannose, has been shown by titration microcalorimetry !o bind to the lectin concanavalin A (ConA) with nearly -6 kcal mol"' greater enthalpy (AH) than methyl cc-D-mannopyranoside (Mandai et al. (1994) Biochemistry 33. 114')) These results indicate that ConA possesses an extended binding site for the trisaccharide. In the present study, we have investigated the binding of a complete set of monodeoxy analogs, two dideoxy analogs and one trideoxy analog of the methyl a-anomer of the trisaccharide to ConA using titration microcalorimetry. The thermodynamic data have identified the 3-, 4- and 6-OH on the n( 1 -6)Man, the 3- and 4-OH on the a(l-3)Man and the 2- and 4-OH on the "core" Man as binding to the lectin These results agree with the recent X-ray crystal structure of the complex of the trimannoside with ConA (Naismith and Field ( 1996)) J. Biol Chem 271. 972) The A AH and AAG values of the deoxy analogs are nonlinear, indicating differential contributions of solvent and protein to the thermodynamics of binding of the analogs. Similar experiments have been carried out with the Man-specific lectin from Dioclea grandiflora.