ADP-forming acetyl-CoA synthetases, functional and structural characterization of novel protein families in archaea and bacteria

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Recently, we identified a novel enzyme in archaea, an ADP-forming acetyl-CoA synthetase (ACD) that catalyses the conversion of acetyl-CoA to acetate and couples this reaction with the synthesis of ATP (acetyl-CoA + ADP + PI ±+ acetate + ATP + HS-CoA). This one-enzyme mechanism of acetate formation is unusual in prokaryotes and appears to be specific to the archaeal domain since all acetate forming bacteria analysed so far utilize the classical two-enzyme mechanism via phosphotransacetylase (PTA) and acetate kinase (AK). However, many of these AK/PTA utilizing bacteria contain ACD homologs of unknown function. ACD enzymes belong to the recently recognized protein superfamily of NDP-forming acyl-CoA synthetases, which also include succinyl-CoA synthetases (SCSs). Within this superfamily, archaeal ACDs and the bacterial ACD homologs constitute distinct subfamilies indicating a domain specific role of bacterial ACD homologs different from acetate formation. In contrast to the well characterized SCSs no information on structure and mechanism of ACD-like enzymes in archaea and bacteria is available so far. Despite similarities between ACDs and SCSs there are several differences in the amino acid sequences as well as the domain architecture of these proteins. Further, most bacterial ACD homologs contain an additional acetyltransferase domain of unknown function, fn this project the unknown bacterial ACD homologs will be characterized to identify their putative physiological function(s). Further, reaction mechanism of ACDs and their structure will be analysed in comparison to SCS. The studies will extend our knowledge of an unusual protein family in central archaeal and bacterial metabolism.