Other
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001oleb...31..403l&link_type=abstract
Origins of Life and Evolution of the Biosphere, v. 31, Issue 4/5, p. 403-434 (2001).
Other
5
Acetogens, Anaerobic, Archaea, Carbon Monoxidedehydrogenase, Chemo-Autotrophic, Methanogens, Origin Of Life, Phylogenetic Analysis
Scientific paper
Acetyl-coenzyme A synthases (ACS) are Ni-Fe-S containing enzymes found in archaea and bacteria. They are divisible into 4 classes. Class I ACS's catalyze the synthesis of acetyl-CoA from CO_2 + 2e^-, CoA, and a methyl group, and contain 5 types of subunits (α, β, γ, δ, and ɛ). Class II enzymes catalyze essentially the reverse reaction and have similar subunit composition. Class III ACS's catalyze the same reaction as Class I enzymes, but use pyruvate as a source of CO_2 and 2e^-, and are composed of 2 autonomous proteins, an α_2β_2 tetramer and a γδ heterodimer. Class IV enzymes catabolize CO to CO_2 and are α-subunit monomers. Phylogenetic analyses were performed on all five subunits. ACS α sequences divided into 2 major groups, including Class I/II sequences and Class III/IV-like sequences. Conserved residues that may function as ligands to the B- and C-clusters were identified. Other residues exclusively conserved in Class I/II sequences may be ligands to additional metal centers in Class I and II enzymes. ACS β sequences also separated into two groups, but they were less divergent than the α's, and the separation was not as distinct. Class III-like β sequences contained ~300 residues at their N-termini absent in Class I/II sequences. Conserved residues identified in β sequences may function as ligands to active site residues used for acetyl-CoA synthesis. ACS γ-sequences separated into 3 groups (Classes I, II, and III), while δ-sequences separated into 2 groups (Class I/II and III). These groups are less divergent than those of α sequences. ACS ɛ-sequence topology showed greater divergence and less consistency vis-à-vis the other subunits, possibly reflecting reduced evolutionary constraints due to the absence of metal centers. The α subunit phylogeny may best reflect the functional diversity of ACS enzymes. Scenarios of how ACS and ACS-containing organisms may have evolved are discussed.
Chang Belinda
Lindahl Paul A.
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