Regulation mechanism of the DsbA/DsbB system that catalyzes disulfine bond formation

在大肠杆菌蛋白二硫键形成途径中，膜蛋白DsbB再氧化还原的周质DsbA，二硫键引入酶。我们的研究结果表明，在有氧生长的大肠杆菌中，二硫键形成的氧化当量是由氧通过呼吸电子传递系统提供的。coli细胞。DsbB中的Cys-41-Val-Leu-Cys-44基序被呼吸醌分子强烈氧化。我们的插入突变的结果表明，一个片段的C-端相邻的CXXC基序是至关重要的呼吸偶联氧化DsbB（4）丙氨酸取代的一个或所有的Ile 45-tyr 46-Glu 47-Arg 48残基，这是由CXXC基序和假定的膜淘选区的法兰，并没有取消呼吸偶联。相反，从该片段中缺失一个或多个残基以及插入一个或多个Ala会严重损害氧化，因此，后一种突变蛋白以还原形式积累或持续特征性的二硫苏糖醇抗性。我们认为Ile 45-tyr 46-Glu 47-Arg 48片段的重要性可能在于其物理长度而不是每个氨基酸的化学性质。CXXC基序相对于膜表面的正确定位对于其与膜锚定的醌分子的有效相互作用至关重要，然后该反应可以由泛醌泛醇与（CXXC）ox/（CXXC）red之间的氧化还原电位之间的巨大差异驱动。

In the Escherichia coli protein disulphide bond formation pathway, a membrane protein DsbB reoxidizes reducd periplasmic DsbA, the disulphide boud-introducing enzyme. Our results indicate that the oxidizing equivalent for disulphide bond formation is provided by oxygen through the respiratory electron transfer system in aerobically growin E. coli cells. The Cys-41-Val-Leu-Cys-44 motif in DsbB is strongly oxidized by respiratory quinone molecules. The results of our insertion mutagenesis indicated that a segment just C-terminally adjacent to CXXC motif is crucial for the respiration-coupled oxidation of DsbB(4)Ala substitution for one or all of the I le45-tyr46-Glu47-Arg48 residues, which are franked by the CXXC motif and the presumed membrane-panning region, did not abolish the respiratory coupling. In contrast,deletion of one or more residues from this segment as well as insertions of one or more Ala into it severely impaired the oxidation.Thus,the latter mutant proteins accumulated as reduced forms or last the characteristic dithiothreitol resistance. We prose that the importance of the Ile45-tyr46-Glu47-Arg48 segment may lie in its physical length rather than the chemical nature of each amino acid. It may be conceivable that a proper positioning of the CXXC motif relative to the membrane surface is crucial for its efficient interaction with membrane-anchored quinonc molecules.The reaction Could then be driven by the large difference between the redox potentials of ubiquinone ubiquinol vs(CXXC)ox/(CXXC)red.