Carbohydrate-induced conformational change in concanavalin A.

Carbohydrate-binding proteins occur widely in the plant kingdom. These proteins, commonly derived from seeds, are called phytohemagglutiuins or lectins (reviewed by Sharon and Lis’). It has become increasingly apparent that lectins can serve as probes for carbohydrate structure and function. The jack-bean lectin, namely, concanavalin A (con A), has received considerable attention because of its diversity of important properties. For example, con A is a potent mitogen2, restores contact inhibition to transformed tissue-culture cells3, induces marked histamine susceptibility in mice4, precipitates polysaccharides and glycoproteins5, and agglutinates several cell-types6. Recently, Edelman et aZ.’ and Hardman and Ainsworth’ determined the tertiary structure of con A. Several authors have presented preliminary evidence for a saccharide-induced, conformational change in con A. Pfiumm er aLg and McCubbin et al. lo showed that con A exhibited changes in its near-ultraviolet circular dichroism spectrum in the presence of carbohydrate ligand. Hassing and Goldstein” found that small concentrations of ligand give rise to changes in the u v. absorption spectra of solutions of con A. Akedo et al.” discovered that certain sugars change the isoelectric point of con A. Additional evidence for ligand-induced, conformational changes is now presented; it is shown that ligand protects con A against hydrolysis by pronase and against heat aggregation. In addition, when con A is tagged with the “reporter” 2-(bromomethyl)+nitrophenol, the ligand induces a visible difference-spectrum.