X-Ray Crystallographic Study of the Quaternary Structure of Canavalin

Abstract

Large rhombohedral crystals of canavalin have been produced through the action of trypsin on a crude aqueous extract of Jack Bean meal. The crystals are of space group R32 with a_hex=136Å and c_hex=75Å (a_rhom=82.4Å and γ=111°). Electrophoresis on SDS-polyacrylamide gels reveals only a single band corresponding to a molecular weight of about 19,500. Since the molecular weight of the molecule in solution has been reported to be 113,000, we conclude from the crystallographic and electrophoretic results that canavalin is a hexamer composed of six identical subunits each of molecular weight 19,500 and arranged according to point group symmetry 32. Metal analysis, though inconclusive, indicates the presence of Mg²⁺, Ca²⁺, and Zn²⁺ in the crystals. Electron micrographs show the crystals to be quite ordered even after dehydration and to show a unique staining pattern.