The bacterial aerobic respiratory chain has a terminal oxidase of the heme-copper oxidase superfamily, comprised of cytochrome c oxidase (COX) and ubiquinol oxidase (UOX); UOX evolved from COX. Acetobacter pasteurianus, an α-Proteobacterial acetic acid bacterium (AAB), produces UOX but not COX, although it has a partial COX gene cluster, ctaBD and ctaA, in addition to the UOX operon cyaBACD. We expressed ctaB and ctaA genes of A. pasteurianus in Escherichia coli and demonstrated their function as heme O and heme A synthases. We also found that the absence of ctaD function is likely due to accumulated mutations. These COX genes are closely related to other α-Proteobacterial COX proteins. However, the UOX operons of AAB are closely related to those of the β/γ-Proteobacteria (γ-type UOX), distinct from the α/β-Proteobacterial proteins (α-type UOX), but different from the other γ-type UOX proteins by the absence of the cyoE heme O synthase. Thus, we suggest that A. pasteurianus has a functional γ-type UOX but has lost the COX genes, with the exception of ctaB and ctaA, which supply the heme O and A moieties for UOX. Our results suggest that, in AAB, COX was replaced by β/γ-Proteobacterial UOX via horizontal gene transfer, while the COX genes, except for the heme O/A synthase genes, were lost.

译文

细菌需氧呼吸链具有血红素铜氧化酶超家族的末端氧化酶,由细胞色素c氧化酶 (COX) 和泛醇氧化酶 (UOX) 组成; UOX从COX进化而来。巴氏杆菌 (Acetobacter pasteurianus) 是一种 α-变形杆菌乙酸细菌 (AAB),除了具有UOX操纵子cyaBACD之外,它还具有部分COX基因簇ctaBD和ctaA,但不产生COX。我们在大肠杆菌中表达了巴氏杆菌的ctaB和ctaA基因,并证明了它们作为血红素O和血红素A合酶的功能。我们还发现,ctaD功能的缺失可能是由于累积的突变。这些COX基因与其他 α-变形菌COX蛋白密切相关。然而,AAB的UOX操纵子与 β/γ-变形菌 (γ 型UOX) 密切相关,与 α/β-变形菌蛋白 (α 型UOX) 不同,但与其他 γ 型UOX蛋白不同的是,不存在cyoE血红素O合酶。因此,我们建议巴氏杆菌具有功能性 γ 型UOX,但已失去COX基因,但ctaB和ctaA除外,后者为UOX提供了血红素O和A部分。我们的结果表明,在AAB中,COX通过水平基因转移被 β/γ-变形杆菌UOX取代,而COX基因 (血红素O/A合酶基因除外) 丢失。

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