1eqb
From Proteopedia
X-RAY CRYSTAL STRUCTURE AT 2.7 ANGSTROMS RESOLUTION OF TERNARY COMPLEX BETWEEN THE Y65F MUTANT OF E-COLI SERINE HYDROXYMETHYLTRANSFERASE, GLYCINE AND 5-FORMYL TETRAHYDROFOLATE
Overview
Crystal structures of human and rabbit cytosolic serine hydroxymethyltransferase have shown that Tyr65 is likely to be a key residue in the mechanism of the enzyme. In the ternary complex of Escherichia coli serine hydroxymethyltransferase with glycine and 5-formyltetrahydrofolate, the hydroxyl of Tyr65 is one of four enzyme side chains within hydrogen-bonding distance of the carboxylate group of the substrate glycine. To probe the role of Tyr65 it was changed by site-directed mutagenesis to Phe65. The three-dimensional structure of the Y65F site mutant was determined and shown to be isomorphous with the wild-type enzyme except for the missing Tyr hydroxyl group. The kinetic properties of this mutant enzyme in catalyzing reactions with serine, glycine, allothreonine, D- and L-alanine, and 5,10-methenyltetrahydrofolate substrates were determined. The properties of the enzyme with D- and L-alanine, glycine in the absence of tetrahydrofolate, and 5, 10-methenyltetrahydrofolate were not significantly changed. However, catalytic activity was greatly decreased for serine and allothreonine cleavage and for the solvent alpha-proton exchange of glycine in the presence of tetrahydrofolate. The decreased catalytic activity for these reactions could be explained by a greater than 2 orders of magnitude increase in affinity of Y65F mutant serine hydroxymethyltransferase for these amino acids bound as the external aldimine. These data are consistent with a role for the Tyr65 hydroxyl group in the conversion of a closed active site to an open structure.
About this Structure
1EQB is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Role of tyrosine 65 in the mechanism of serine hydroxymethyltransferase., Contestabile R, Angelaccio S, Bossa F, Wright HT, Scarsdale N, Kazanina G, Schirch V, Biochemistry. 2000 Jun 27;39(25):7492-500. PMID:10858298 Page seeded by OCA on Fri May 2 15:24:12 2008
