Lindahl P A, Chang B
Departments of Chemistry and of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-3255, USA.
Orig Life Evol Biosph. 2001 Aug-Oct;31(4-5):403-34. doi: 10.1023/a:1011809430237.
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 CO2 + 2e-, CoA, and a methyl group, and contain 5 types of subunits (alpha, beta, gamma, delta, and epsilon). 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 CO2 and 2e-, and are composed of 2 autonomous proteins, an alpha 2 beta 2 tetramer and a gamma delta heterodimer. Class IV enzymes catabolize CO to CO2 and are alpha-subunit monomers. Phylogenetic analyses were performed on all five subunits. ACS alpha 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 beta sequences also separated into two groups, but they were less divergent than the alpha's, and the separation was not as distinct. Class III-like beta sequences contained approximately 300 residues at their N-termini absent in Class I/II sequences. Conserved residues identified in beta sequences may function as ligands to active site residues used for acetyl-CoA synthesis. ACS gamma-sequences separated into 3 groups (Classes I, II, and III), while delta-sequences separated into 2 groups (Class I/II and III). These groups are less divergent than those of alpha sequences. ACS epsilon-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 alpha subunit phylogeny may best reflect the functional diversity of ACS enzymes. Scenarios of how ACS and ACS-containing organisms may have evolved are discussed.
乙酰辅酶A合成酶（ACS）是存在于古细菌和细菌中的含镍铁硫酶。它们可分为4类。I类ACS催化由二氧化碳 + 2个电子、辅酶A和一个甲基合成乙酰辅酶A，含有5种亚基（α、β、γ、δ和ε）。II类酶催化基本上相反的反应，且具有相似的亚基组成。III类ACS催化与I类酶相同的反应，但使用丙酮酸作为二氧化碳和2个电子的来源，由2种自主蛋白质组成，即α2β2四聚体和γδ异二聚体。IV类酶将一氧化碳分解为二氧化碳，是α亚基单体。对所有5种亚基进行了系统发育分析。ACS α序列分为2个主要组，包括I/II类序列和III/IV类样序列。鉴定出了可能作为B簇和C簇配体的保守残基。在I/II类序列中专门保守的其他残基可能是I类和II类酶中其他金属中心的配体。ACS β序列也分为两组，但它们的差异比α序列小，且分组不那么明显。III类样β序列在其N端含有约300个I/II类序列中不存在的残基。在β序列中鉴定出的保守残基可能作为用于乙酰辅酶A合成的活性位点残基的配体。ACS γ序列分为3组（I类、II类和III类），而δ序列分为2组（I/II类和III类）。这些组的差异比α序列的差异小。ACS ε序列拓扑结构相对于其他亚基显示出更大的差异和更低的一致性，这可能反映了由于缺乏金属中心而导致的进化限制减少。α亚基系统发育可能最能反映ACS酶的功能多样性。讨论了ACS和含ACS生物可能的进化情况。
