Kletzin A, Adams M W
Department of Biochemistry, University of Georgia, Athens 30602, USA.
J Bacteriol. 1996 Jan;178(1):248-57. doi: 10.1128/jb.178.1.248-257.1996.
Previous studies have shown that the hyperthermophilic archaeon Pyrococcus furiosus contains four distinct cytoplasmic 2-ketoacid oxidoreductases (ORs) which differ in their substrate specificities, while the hyperthermophilic bacterium Thermotoga maritima contains only one, pyruvate ferredoxin oxidoreductase (POR). These enzymes catalyze the synthesis of the acyl (or aryl) coenzyme A derivative in a thiamine PPi-dependent oxidative decarboxylation reaction with reduction of ferredoxin. We report here on the molecular analysis of the POR (por) and 2-ketoisovalerate ferredoxin oxidoreductase (vor) genes from P. furiosus and of the POR gene from T. maritima, all of which comprise four different subunits. The operon organization for P. furiosus POR and VOR was porG-vorDAB-porDAB, wherein the gamma subunit is shared by the two enzymes. The operon organization for T. maritima POR was porGDAB. The three enzymes were 46 to 53% identical at the amino acid level. Their delta subunits each contained two ferredoxin-type [4Fe-4S] cluster binding motifs (CXXCXXCXXXCP), while their beta subunits each contained four conserved cysteines in addition to a thiamine PPi-binding domain. Amino-terminal sequence comparisons show that POR, VOR, indolepyruvate OR, and 2-ketoglutarate OR of P. furiosus all belong to a phylogenetically homologous OR family. Moreover, the single-subunit pyruvate ORs from mesophilic and moderately thermophilic bacteria and from an amitochondriate eucaryote each contain four domains which are phylogenetically homologous to the four subunits of the hyperthermophilic ORs (27% sequence identity). Three of these subunits are also homologous to the dimeric POR from a mesophilic archaeon, Halobacterium halobium (21% identity). A model is proposed to account for the observed phenotypes based on genomic rearrangements of four ancestral OR subunits.
先前的研究表明，嗜热古菌激烈火球菌含有四种不同的胞质2-酮酸氧化还原酶（ORs），它们的底物特异性不同，而嗜热细菌海栖热袍菌仅含有一种，即丙酮酸铁氧化还原酶（POR）。这些酶在硫胺焦磷酸依赖的氧化脱羧反应中催化酰基（或芳基）辅酶A衍生物的合成，并伴有铁氧化还原蛋白的还原。我们在此报告了来自激烈火球菌的POR（por）和2-酮异戊酸铁氧化还原酶（vor）基因以及来自海栖热袍菌的POR基因的分子分析，所有这些基因均由四个不同的亚基组成。激烈火球菌POR和VOR的操纵子组织为porG-vorDAB-porDAB，其中γ亚基由这两种酶共享。海栖热袍菌POR的操纵子组织为porGDAB。这三种酶在氨基酸水平上有46%至53%的同一性。它们的δ亚基各自包含两个铁氧化还原蛋白型[4Fe-4S]簇结合基序（CXXCXXCXXXCP），而它们的β亚基除了硫胺焦磷酸结合域外各自还包含四个保守的半胱氨酸。氨基末端序列比较表明，激烈火球菌的POR、VOR、吲哚丙酮酸OR和2-酮戊二酸OR都属于系统发育同源的OR家族。此外，来自嗜温和中度嗜热细菌以及无线粒体真核生物的单亚基丙酮酸OR各自包含四个与嗜热OR的四个亚基系统发育同源的结构域（序列同一性为27%）。这些亚基中的三个也与嗜温古菌嗜盐嗜盐杆菌的二聚体POR同源（同一性为21%）。基于四个祖先OR亚基的基因组重排，提出了一个模型来解释观察到的表型。
