Cytochrome bd-type oxygen reductases (cytbd) belong to one of three enzyme superfamilies that catalyze oxygen reduction to water. They are widely distributed in Bacteria and Archaea, but the full extent of their biochemical diversity is unknown. Here we used phylogenomics to identify 3 families and several subfamilies within the cytbd superfamily. The core architecture shared by all members of the superfamily consists of four transmembrane helices that bind two active site hemes, which are responsible for oxygen reduction. While previously characterized cytochrome bd-type oxygen reductases use quinol as an electron donor to reduce oxygen, sequence analysis shows that only one of the identified families has a conserved quinol binding site. The other families are missing this feature, suggesting that they use an alternative electron donor. Multiple gene duplication events were identified within the superfamily, resulting in significant evolutionary and structural diversity. The CydAA cytbd, found exclusively in Archaea, is formed by the co-association of two superfamily paralogs. We heterologously expressed CydAA from Caldivirga maquilingensis and demonstrated that it performs oxygen reduction with quinol as an electron donor. Strikingly, CydAA is the first isoform of cytbd containing only b-type hemes shown to be active when isolated, demonstrating that oxygen reductase activity in this superfamily is not dependent on heme d.

中文翻译：

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细胞色素bd型氧还原酶超家族的进化及cydAA在古细菌中的功能

细胞色素bd型氧还原酶（cytbd）属于催化将氧还原为水的三个酶超家族之一。它们广泛分布于细菌和古细菌中，但其生化多样性的全部范围尚不清楚。在这里，我们使用系统发育组学来识别cytbd超家族中的3个家族和几个亚家族。超家族所有成员共有的核心结构由四个跨膜螺旋组成，这些螺旋结合两个活性位点血红素，负责氧的还原。虽然先前表征的细胞色素bd型氧还原酶使用奎奴尔作为电子供体来减少氧气，但序列分析显示，只有一个已鉴定的家族具有保守的奎奴尔结合位点。其他家庭则缺少此功能，这表明他们使用了替代电子供体。在超家族中鉴定出多个基因重复事件，导致显着的进化和结构多样性。CydAA cytbd仅在古细菌中发现，是由两个超家族旁系同源物共同结合而成。我们异源表达了来自Caldivirga maquilingensis的CydAA，并证明它以喹诺醇为电子供体进行了氧还原。引人注目的是，CydAA是cytbd的第一个同工型，仅包含b型血红素，在分离时显示出活性，表明该超家族中的氧还原酶活性不依赖血红素d。我们异源表达了来自Caldivirga maquilingensis的CydAA，并证明它以喹诺醇为电子供体进行了氧还原。引人注目的是，CydAA是cytbd的第一个同工型，仅含有b型血红素，在分离时显示出活性，表明该超家族中的氧还原酶活性不依赖血红素d。我们异源表达了来自Caldivirga maquilingensis的CydAA，并证明它以喹诺醇为电子供体进行了氧还原。引人注目的是，CydAA是cytbd的第一个同工型，仅含有b型血红素，在分离时显示出活性，表明该超家族中的氧还原酶活性不依赖血红素d。