The Role of O-acetylserine Sulfhydrylase in Cysteine Biosynt

A structural and functional Analysis

Pyridoxial 5’-phosphate (PLP) acts as a cofactor in many enzymes involved in diverse aspects of amino acid metabolism such as transamination, β/γ-elimination, β/γ-replacement and racemization. In all PLP-dependant enzymes the carbonyl group of the PLP coenzyme binds to an ε-amino group of a lysine residue in the active site, forming an internal aldimine. O-Acetylserine sulfahydrylase (OASS), isolated from Salmonella typhimurium, belongs to the β -family of PLP-dependant enzymes and catalyzes the last step in the cysteine biosynthesis pathway via β-replacement, converting O-acetylserine (OAS) to cysteine, upon exchanging acetate in the OAS side chain for sulfide (Fig. 1). The structural and functional framework underlying the reaction mechanism for OASS has been characterized extensively by kinetic studies, site-directed mutagenesis, UV-visible fluorescence and phosphorescence spectroscopy and x-ray structural determination. Three conformationally distinct “open”, “closed”, and “inhibited” states were elucidated.

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Some common words found in the essay are:
Proximity Pro36, Protein Folding, Conformational Changes, N-terminus C-terminus, Gly178 Thr180, McClure Cook, Dynamic AOSS, Concluding Remarks, Topology Understanding, SH- Catalytic, et al, burkhard et al, active site, burkhard et, et al 1996, closed conformation, al 1996, schiff base, conformational changes, amino acid, free energy, inhibited conformation, schiff base linkage, et al 2000, strambini et al,
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