Loop Residues and Catalysis in OMP Synthase

Loop residues and catalysis in OMP synthase.

Residue-to-alanine mutations and a two-amino acid deletion have been made in the highly conserved catalytic loop (residues 100-109) of Salmonella typhimurium OMP synthase (orotate phosphoribosyltransferase, EC 2.4.2.10). As described previously, the K103A mutant enzyme exhibited a 10(4)-fold decrease in k(cat)/K(M) for PRPP; the K100A enzyme suffered a 50-fold decrease. Alanine mutations at His...

Motional dynamics of the catalytic loop in OMP synthase.

In de novo pyrimidine biosynthesis, orotate phosphoribosyltransferase catalyzes the formation of orotidine 5'-monophosphate (OMP) from orotic acid and alpha-D-5-phosphoribosyl-1-pyrophosphate (PRPP). The known three-dimensional structure of the dimeric enzyme from Salmonella typhimurium is similar to that of other Type I phosphoribosyltransferases (nucleotide synthases) with a solvent-exposed a...

Abietadiene synthase catalysis: conserved residues involved in protonation-initiated cyclization of geranylgeranyl diphosphate to (+)-copalyl diphosphate.

Abietadiene synthase catalyzes two sequential, mechanistically distinct cyclization reactions in the formation of a mixture of abietadiene double bond isomers as the committed step in resin acid biosynthesis. Each reaction is carried out at a separate active site residing in a structurally distinct domain, and the reactions are kinetically separable. The first cyclization reaction is initiated ...

Substrate Controlled Divergence in Polyketide Synthase Catalysis

Biochemical characterization of polyketide synthases (PKSs) has relied on synthetic substrates functionalized as electrophilic esters to acylate the enzyme and initiate the catalytic cycle. In these efforts, N-acetylcysteamine thioesters have typically been employed for in vitro studies of full PKS modules as well as excised domains. However, substrate engineering approaches to control the cata...

Global Residues and Two-Loop Hepta-Cuts