Darby N J, Raina S, Creighton T E
European Molecular Biology Laboratory, Heidelberg, Germany.
Biochemistry. 1998 Jan 20;37(3):783-91. doi: 10.1021/bi971888f.
DsbA and DsbC are involved in protein disulfide bond formation in the periplasm of Gram-negative bacteria. The two proteins are thought to fulfill different functions in vivo, DsbA as a catalyst of disulfide bond formation and DsbC as a catalyst of disulfide bond rearrangement. To explore the basis of this catalytic complementarity, the reaction mechanism of DsbC has been examined using unstructured model peptides that contain only one or two cysteine residues as substrates. The reactions between the various forms of the peptide and DsbC occur at rates up to 10(6)-fold faster than those that involve glutathione and DsbC, and they were constrained to occur at only one sulfur atom of disulfide bonds involving the peptide. Mixed disulfide complexes of DsbC and the peptide were 10(4)-fold more stable than the corresponding mixed disulfides with glutathione. These observations suggest that noncovalent binding interactions occur between the peptide and DsbC, which contribute to the very rapid kinetics of substrate utilization. The interactions between DsbC and the peptide appear to be more substantial than those between DsbA and the same peptide. The differences in the reaction of the peptide at the active sites of DsbA and DsbC provide insight into why DsbC is the better catalyst of disulfide bond rearrangement and how the active site chemistry of these structurally related proteins has been adapted to fulfill complementary functions.
DsbA和DsbC参与革兰氏阴性菌周质中蛋白质二硫键的形成。这两种蛋白质在体内被认为具有不同的功能，DsbA作为二硫键形成的催化剂，而DsbC作为二硫键重排的催化剂。为了探究这种催化互补性的基础，已使用仅含有一个或两个半胱氨酸残基的无结构模型肽作为底物来研究DsbC的反应机制。肽的各种形式与DsbC之间的反应速率比涉及谷胱甘肽和DsbC的反应速率快高达10^6倍，并且它们被限制仅在涉及肽的二硫键的一个硫原子处发生。DsbC与肽的混合二硫复合物比与谷胱甘肽的相应混合二硫复合物稳定10^4倍。这些观察结果表明，肽与DsbC之间发生非共价结合相互作用，这有助于底物利用的非常快速的动力学。DsbC与肽之间的相互作用似乎比DsbA与同一肽之间的相互作用更显著。肽在DsbA和DsbC活性位点的反应差异有助于理解为什么DsbC是更好的二硫键重排催化剂，以及这些结构相关蛋白质的活性位点化学如何被调整以实现互补功能。
