Carbohydrate specificity of pea lectin revealed by X-ray analysis

Structures of two new crystal complexes of pea lectin (Pisum sativum,dimer, molecular mass ca. 50 kDa) with D-glucopyranose (P2(1)2(1)2(1), space grou p; unit cell parameters: a 73.4, b 107.7, and c 64.6 Angstrom) and D-mannop yranose (P2(1)2(1)2(1); a 62.6, b 135.1,and c 54.9 Angstrom) were solved by the molecular replacement approach at 2.3 and 1.98 Angstrom resolutions an d refined to the R factor values of 0.155 and 0.217, respectively. The comp arative analysis of the structures found and those determined earlier showe d pea lectin to bind the alpha- and beta-forms of monosaccharides in a rati o close to that in solution. Stereochemical features of the carbohydrate sp ecificity of pea lectin were studied, and a statistical-dynamic model of th e carbohydrate binding was developed using energy computation methods. This model enables the evaluation of the region of the monosaccharide interacti on with the protein carbohydrate-binding site and the ensemble of the carbo hydrate orientations providing for its productive binding. Amino acid subst itutions, Asn39-->Gln and Asn39-->Lys, capable to cause directed changes in the lectin binding specificity toward the cognate carbohydrates were propo sed.