Department of Biological Sciences, Towson University, Towson, Maryland, USA.
J Bacteriol. 2013 Aug;195(16):3640-50. doi: 10.1128/JB.00324-13. Epub 2013 Jun 7.
Cytochrome bd oxidase operons from more than 50 species of bacteria contain a short gene encoding a small protein that ranges from ∼30 to 50 amino acids and is predicted to localize to the cell membrane. Although cytochrome bd oxidases have been studied for more than 70 years, little is known about the role of this small protein, denoted CydX, in oxidase activity. Here we report that Escherichia coli mutants lacking CydX exhibit phenotypes associated with reduced oxidase activity. In addition, cell membrane extracts from ΔcydX mutant strains have reduced oxidase activity in vitro. Consistent with data showing that CydX is required for cytochrome bd oxidase activity, copurification experiments indicate that CydX interacts with the CydAB cytochrome bd oxidase complex. Together, these data support the hypothesis that CydX is a subunit of the CydAB cytochrome bd oxidase complex that is required for complex activity. The results of mutation analysis of CydX suggest that few individual amino acids in the small protein are essential for function, at least in the context of protein overexpression. In addition, the results of analysis of the paralogous small transmembrane protein AppX show that the two proteins could have some overlapping functionality in the cell and that both have the potential to interact with the CydAB complex.
来自 50 多种细菌的细胞色素 bd 氧化酶操纵子包含一个短基因，该基因编码一种小蛋白，其大小约为 30 到 50 个氨基酸，预测定位于细胞膜。尽管细胞色素 bd 氧化酶已经研究了 70 多年，但对于这种小蛋白（称为 CydX）在氧化酶活性中的作用知之甚少。在这里，我们报告说缺乏 CydX 的大肠杆菌突变体表现出与氧化酶活性降低相关的表型。此外，来自 ΔcydX 突变株的细胞膜提取物在体外具有降低的氧化酶活性。与表明 CydX 是细胞色素 bd 氧化酶活性所必需的数据一致，共纯化实验表明 CydX 与 CydAB 细胞色素 bd 氧化酶复合物相互作用。这些数据共同支持了 CydX 是 CydAB 细胞色素 bd 氧化酶复合物的一个亚基的假说，该亚基是复合物活性所必需的。对 CydX 的突变分析结果表明，该小蛋白中的少数个别氨基酸对于功能是必不可少的，至少在蛋白过表达的情况下是这样。此外，对类似的小跨膜蛋白 AppX 的分析结果表明，这两种蛋白在细胞中可能具有一些重叠的功能，并且都有可能与 CydAB 复合物相互作用。
