Identification of a cysteine involved in the interaction between carbon monoxide dehydrogenase and corrinoid/Fe‐S protein from Clostridium thermoaceticum

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Abstract
In Clostridium thermoaceticum, the synthesis of acetyl‐CoA from methyl tetrahydrofolate occurs via a series of enzymatic reactions involving methyl transferase, corrinoid/Fe‐S protein (corrinoid), carbon monoxide dehydrogenase (CODH) and ferredoxin. We have investigated the possibility of one or more of these proteins existing as multi‐enzyme complexes in vivo with higher catalytic activity. A protein complex consisting of CODH and corrinoid was isolated from the cell‐free extracts of Clostridium thermoaceticum. The acetyl‐CoA synthesis was found to be ∼ 1.8‐fold higher with the complex than that observed with the isolated protein components. HPLC gel filtration analyses of the native and DTE reduced complex suggested that the CODH:corrinoid complex is held together primarily by an inter disulfide bond. By differential labeling of thiols with [14C]N‐ethylmaleimide it was found that Cys‐506 of the α subunit of CODH was involved in the disulfide linkage with the corrinoid of the complex.