Nitrilase Structure and Mechanism

Brenner [41] showed that a nitrilase folded protein consisted of a polypeptide of a-helices and p-sheets that formed a novel a-p-p-a sandwich fold, with a triad of residues in the active site (Glu-Lys-Cys) essential for the covalent catalysis. Structural eluddation of a nitrilase produced by Rhodococcus rhodochrous J1 showed that it formed a multimeric extended hehx [42]. 

Mahadevan and Thimann [43] postulated the first nitrilase reaction mechanism, suggesting that the nitrile carbon present in the substrate displays a partial positive charge that is subjed to nudeophihc attack by one of the two SH groups in the nitrilase active site. The resulting thioimidate is then hydrolyzed to a thioester, with the release of ammonia as a by-product Hydrolysis of the acyl-enzyme then results in the release of the final acid product. 

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