A Three-Dimensional Homology Model of the O-Acetylserine Sulfhydrylase-B from Salmonella typhimurium

Title: A Three-Dimensional Homology Model of the O-Acetylserine Sulfhydrylase-B from Salmonella typhimurium

Volume: 13 Issue: 1

Author(s): W. M. Rabeh, T. Mather and P. F. Cook

Affiliation:

Keywords: A-isozyme, cysteine, homologous enzymes, asparagines loop, Schiff base, Structurally conserved regions

Abstract: O-acetylserine sulfhydrylase (OASS) catalyzes the last step in the cysteine biosynthetic pathway in enteric bacteria and plants. The overall pathway involves the substitution of the β-acetoxy group of O-acetyl-L-serine with inorganic bisulfide. Two isozymes are present in S. typhimurium, the A- and B-isozymes, expressed under aerobic and anaerobic conditions, respectively. No crystal structure is presently available for the B-isozyme. Kinetic data indicate the catalytic mechanism of OASS-B is ping-pong, as found for the A-isozyme, but kinetic parameters and substrate specificity differ. In order to estimate whether structural differences may be responsible for the kinetic differences, a homology model was built using the structure of OASS-A as the template for the OASS-B model. The β- subunit of tryptophan synthase and cystathionine β-synthase were used for comparison. Differences between the OASS-A structure and the homology model for OASS-B are discussed.

Cite this article as:

Rabeh M. W., Mather T. and Cook F. P., A Three-Dimensional Homology Model of the O-Acetylserine Sulfhydrylase-B from Salmonella typhimurium, Protein & Peptide Letters 2006; 13 (1) . https://dx.doi.org/10.2174/092986606774502126