Sequential Oxidations of Thiolates and the Cobalt Metallocenter in a Synthetic Metallopeptide: Implications for the Biosynthesis of Nitrile Hydratase

Dutta, Arnab, Flores, Marco, Roy, Souvik , Schmitt, Jennifer C., Hamilton, G. Alexander, Hartnett, Hilairy E., Shearer, Jason M. and Jones, Anne K. (2013) Sequential Oxidations of Thiolates and the Cobalt Metallocenter in a Synthetic Metallopeptide: Implications for the Biosynthesis of Nitrile Hydratase. Inorganic Chemistry, 52 (9). pp. 5236-5245. ISSN 0020-1669

Full content URL: https://doi.org/10.1021/ic400171z

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Item Type:Article
Item Status:Live Archive

Abstract

Cobalt nitrile hydratases (Co-NHase) contain a catalytic cobalt(III) ion coordinated in an N2S3 first coordination sphere composed of two amidate nitrogens and three cysteine-derived sulfur donors: a thiolate (-SR), a sulfenate (-S(R)O–), and a sulfinate (-S(R)O2–). The sequence of biosynthetic reactions that leads to the post-translational oxidations of the metal and the sulfur ligands is unknown, but the process is believed to be initiated directly by oxygen. Herein we utilize cobalt bound in an N2S2 first coordination sphere by a seven amino acid peptide known as SODA (ACDLPCG) to model this oxidation process. Upon exposure to oxygen, Co-SODA is oxidized in two steps. In the first fast step (seconds), magnetic susceptibility measurements demonstrated that the metallocenter remains paramagnetic, that is, Co2+, and sulfur K-edge X-ray absorption spectroscopy (XAS) is used to show that one of the thiolates is oxidized to sulfinate. In a second process on a longer time scale (hours), magnetic susceptibility measurements and Co K-edge XAS show that the metal is oxidized to Co3+. Unlike other model complexes, additional slow oxidation of the second thiolate in Co-SODA is not observed, and a catalytically active complex is never formed. The likely reason is the absence of the axial thiolate ligand. In essence, the reactivity of Co-SODA can be described as between previously described models which either quickly convert to final product or are stable in air, and it offers a first glimpse into a possible oxidation pathway for nitrile hydratase biosynthesis.

Keywords:Peptides and proteins, Metals, Ligands, Oxidation Thiolates
Subjects:F Physical Sciences > F120 Inorganic Chemistry
C Biological Sciences > C720 Biological Chemistry
F Physical Sciences > F100 Chemistry
C Biological Sciences > C700 Molecular Biology, Biophysics and Biochemistry
Divisions:College of Science > School of Chemistry
ID Code:40685
Deposited On:16 Apr 2020 15:44

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