Magnetic resonance studies of concanavalin A:CONFORMATIONAL CHANGES INDUCED BY Ca2+ and...

Three independent solution spectroscopic techniques (solvent proton relaxation enhancement, circular dichroism, and high resolution 220 MHz proton magnetic resonance spectroscopy) have been utilized to demonstrate mental ion- and monosaccharide inhibitor-induced structural perturbations for the dimeric form of the plant lectin concanavalin A (Con A). The results indicate that (i) the occupation of the transition metal ion site S1 by Mn-2+ or Zn-2+ does not detectably perturn the demetallized protein conformation, (ii) the binding of Ca=2+ to the Con A-Mn-2+ or Con A-Zn-2+ complexes perturbs the protein structure in the vicinity of the S1 site as well as at points remote from the S1-S2 double ion site, and (iii) the binding of the monosaccharide inhibitor alpha-methyl-D-mannopyranoside to the fully metallized Con A complex also significantly perturbs the structural features of the protein. A detailed radio frequency dependence analysis of the Ca-2+ effect on the solvent proton relaxation enhancement properties of the Con A-Mn-2+ complex indicates that the considerable reduction in the observed enhancement upon Ca-2+ binding principally results from an approximate 120-fold decrease in the single Mn-2+ water of hydratio- exchange rate; The 220 MHz proton magnetic resonance spectra for Con A indicate that this form of spectroscopy is the most useful of those utilized in detailing the solution structural features of this lectin, and a tentative assignment for the C-2-H proton of histidine residue 24 (the S1 site ligand) has been proposed.