Molecular Shape and Packing in Crystals of Soybean β-Amylase

Abstract

The structure of soybean β-amylase in trigonal (P3₂21) crystals was determined at 4.5 A resolution by X-ray crystallographic techniques using the isomorphous replacement method. X Ray diffraction data were collected by the screened precession method for the native enzymeand two heavy atom derivatives. The shape of the enzymemolecule and the locations of mercurial binding are presented. The molecule appeared to be composed of two domains: the larger domain contains one mercurial site on its surface and the smaller domainhas another mercurial site, which seemed to be the so-called essential sulfhydryl group. A distinct cleft formed between the domains near the latter sulfhydryl group maybe a substrate binding region.