Biochemical and X-Ray Diffraction Analysis of Concanavalin B Crystals from Jack Bean

Abstract

Parallel biochemical and crystallographic studies have been carried out on the protein concanavalin B from Jack Bean (Canavalis ensiformis). The studies show the protein to be a monomer of 33,000 daltons with unexceptional amino acid composition and no covalently bound carbohydrate. The molecule contains a single, firmly bound zinc ion and we present evidence that the protein specifically binds nucleotide coenzymes including at least NADPH and flavin mononucleotide. An electron density map of the concanavalin B crystals (space group P6₁, a = b = 80.9 Å, c = 102.2 Å) has been calculated from phases based on six isomorphous heavy atom derivatives. A description of the structure of the protein based on the 5.0 Å resolution x-ray diffraction study is provided. The structure appears to contain a substantial amount of α-helix as well as an extensive β-sheet and these are organized into two domains of unequal size. The position of the bound zinc is indicated by anomalous difference Fouriers and the nucleotide binding site by conventional difference Fourier maps.