DIOCLEINAE LECTINS ARE A GROUP OF PROTEINS WITH CONSERVED BINDING-SITES FOR THE CORE TRIMANNOSIDE OF ASPARAGINE-LINKED OLIGOSACCHARIDES ANDDIFFERENTIAL SPECIFICITIES FOR COMPLEX CARBOHYDRATES

The seed lectin from Dioclea grandiflora and jack, bean lectin concana valin A (ConA) are both members of the Diocleinae subtribe of Legumino sae lectins. Both lectins have recently been shown to possess enhanced affinities and extended binding sites for the trisaccharide, 3,6-di-O -(alpha-D-mannopyranosyl)-D-mannose which is present in the core regio n of all asparagine-linked carbohydrates (Gupta, D., Oscarson, S., Raj u, S., Stanley, P. Toone, E. J. and Brewer, C. F. (1996) Eur. J. Bioch em, 242, 320-326). In the present study, the binding specificities of seven other lectins from the Diocleinae subtribe have been investigate d by hemagglutination inhibition and isothermal titration microcalorim etry (ITC). The lectins are from Canavalia brasiliensis, Canavalia bon ariensis, Cratylia floribunda, Dioclea rostrata, Dioclea virgata, Dioc lea violacea, and Dioclea guianensis. Hemagglutination inhibition and ITC experiments show that all seven lectins are Man/Glc-specific and h ave high affinities for the core trimannoside, like ConA and D. grandi flora lectin. All seven lectins also exhibit the same pattern of bindi ng to a series of monodeoxy analogs and a tetradeoxy analog of the tri mannoside, similar to that of ConA and D. grandiflora lectin. However, C. bonariensis, C. floribunda, D. rostrata, and D. violacea, like D. grandiflora, show substantially reduced affinities for a biantennary c omplex carbohydrate with terminal GlcNAc residues, while C. brasiliens is, D. guianensis, and D. virgata, Like ConA, exhibit affinities for t he oligosaccharide comparable with that of the trimannoside. Thermodyn amic data obtained by ITC indicate different energetic mechanisms of b inding of the above two groups of lectins to the complex carbohydrate. The ability of the lectins to induce histamine release from rat perit oneal mast cells is shown to correlate with the relative affinities of the proteins for the biantennary carbohydrate.