Cytochromes bd are ubiquitous amongst prokaryotes including many human-pathogenic bacteria. Such complexes are targets for the development of antimicrobial drugs. However, an understanding of the relationship between the structure and functional mechanisms of these oxidases is incomplete. Here, we have determined the 2.8 Å structure of Mycobacterium smegmatis cytochrome bd by single-particle cryo-electron microscopy. This bd oxidase consists of two subunits CydA and CydB, that adopt a pseudo two-fold symmetrical arrangement. The structural topology of its Q-loop domain, whose function is to bind the substrate, quinol, is significantly different compared to the C-terminal region reported for cytochromes bd from Geobacillus thermodenitrificans (G. th) and Escherichia coli (E. coli). In addition, we have identified two potential oxygen access channels in the structure and shown that similar tunnels also exist in G. th and E. coli cytochromes bd. This study provides insights to develop a framework for the rational design of antituberculosis compounds that block the oxygen access channels of this oxidase.

细胞色素bd在原核生物中无处不在，包括许多人类致病细菌。这种复合物是开发抗微生物药物的目标。然而，对这些氧化酶的结构和功能机制之间的关系的理解是不完整的。在这里，我们通过单粒子冷冻电子显微镜确定了耻垢分枝杆菌细胞色素bd的 2.8 Å 结构。该bd氧化酶由两个亚基 CydA 和 CydB 组成，它们采用伪二重对称排列。与细胞色素bd报道的 C 末端区域相比，其 Q 环结构域的结构拓扑结构显着不同，其功能是结合底物醌醇从土芽孢thermodenitrificans（G.个）和大肠埃希氏菌（大肠杆菌）。此外，我们在结构中确定了两个潜在的氧气通道，并表明G.th和大肠杆菌细胞色素bd 中也存在类似的隧道。这项研究为开发可阻断这种氧化酶氧气进入通道的抗结核化合物的合理设计框架提供了见解。