CRYSTAL FORMS AND SUBUNIT STOICHIOMETRY OF SERINE HYDROXYMETHYLTRANSFERASE

Serine hydroxymethyltransferase catalyzes the formation of one-carbon units essential for anabolic processes leading to the formation of suc h essential cellular components as purines, pyrimidines, amino acids, and lipids. Crystal structure determinations of several forms of the e nzyme are under way, and to expand the comparative scope of these stud ies, we have crystallized the rabbit cytosolic and mitochondrial enzym es. Crystallization of serine hydroxymethyltransferase from different sources has often been problematic, and we report studies addressing t hese difficulties that may have more general application. The crystal lattice symmetry and the stoichiometry of the crystal asymmetric units and of the enzyme in solution suggest that serine hydroxymethyltransf erase may exist as dimers, trimers, and possibly higher order complexe s and that their aggregation state is affected by ionic strength. (C) 1998 Academic Press.