title: A three-dimensional homology model of the O-acetylserine sulfhydrylase-B from Salmonella typhimurium.
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 beta-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 beta-subunit of tryptophan synthase and cystathionine beta-synthase were used for comparison. Differences between the OASS-A structure and the homology model for OASS-B are discussed.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019, USA.
authors.forename: Wael M
authors.initials: WM
authors.lastname: Rabeh
authors.forename: Timothy
authors.initials: T
authors.lastname: Mather
authors.forename: Paul F
authors.initials: PF
authors.lastname: Cook
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D003547:Cysteine Synthase / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid
chemical_list: D003547:Cysteine Synthase