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

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

Journal Name: Protein & Peptide Letters

Volume 13 , Issue 1 , 2006

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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.

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

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Article Details

VOLUME: 13
ISSUE: 1
Year: 2006
Page: [7 - 13]
Pages: 7
DOI: 10.2174/092986606774502126

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