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Publication Abstract from PubMed

Carbonyl sulfide (COS) is an atmospheric trace gas leading to sulfate aerosol formation and, thereby, participating in the global radiation balance and ozone chemistry, but its biological sinks are not well understood. Thiobacillus thioparus strain THI115 can grow on thiocyanate (SCN(-)) as its sole energy source. Previously, we showed that SCN(-) is first converted to COS by thiocyanate hydrolase in T. thioparus strain THI115. In the present work, we purified, characterized and determined the crystal structure of carbonyl sulfide hydrolase (COSase), which is responsible for the degradation of COS to H(2)S and CO(2), the second step of SCN(-) assimilation. COSase is a homotetramer composed of a 23.4 kDa subunit containing a zinc ion in its catalytic site. The amino acid sequence of COSase is homologous to the beta-class carbonic anhydrases (beta-CAs). Although the crystal structure including the catalytic site resembles those of the beta-CAs, COSase exhibited no CO(2) hydration activity. The alpha5 helix and the extra loop (Gly150-Pro158) near the N-terminus of the alpha6 helix narrow the substrate pathway, which likely controls substrate specificity. The k(cat)/K(m) value, 1.1x10(6) s(-1)M(-1), is comparable to those of the beta-CAs. COSase hydrolyzes COS over a wide concentration range, including the ambient level, in vitro and in vivo. COSase and its structurally related enzymes are distributed in the clade D in the phylogenetic tree of beta-CAs, suggesting that COSase and its related enzymes are one of the catalysts responsible for the global sink of COS.

Carbonyl sulfide hydrolase is an enzyme required for chemolithotrophic growth of Thiobacillus thioparus strain THI115 with thiocyanate.,Ogawa T, Noguchi K, Saito M, Nagahata Y, Kato H, Ohtaki A, Nakayama H, Dohmae N, Matsushita Y, Odaka M, Yohda M, Nyunoya H, Katayama Y J Am Chem Soc. 2013 Feb 13. PMID:23406161^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.