脯氨酸-77 取代天冬氨酸对菌紫质光驱动质子释放的影响。

Effect of substitution of proline-77 to aspartate on the light-driven proton release of bacteriorhodopsin.

机构信息

State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Advanced Materials Laboratory, Fudan University, Shanghai, China.

出版信息

Photochem Photobiol. 2012 Jul-Aug;88(4):922-7. doi: 10.1111/j.1751-1097.2012.01146.x. Epub 2012 Apr 24.

DOI:10.1111/j.1751-1097.2012.01146.x

PMID:22443335

Abstract

Wild-type bacteriorhodopsin (BR) and another retinal protein archaerhodopsin 4 (AR4) are both light-driven proton pumps, but exhibit opposite temporal orders of proton release and uptake upon a flash illumination at neutral pH due to a higher pK(a) of proton release complex (PRC) in AR4. Since the 77th residue in the extracellular side is proline (P) in BR, but aspartic acid (D) in AR4, we have mutated P77 in BR by D in this study. The new point mutation was found to affect the kinetics of proton release and the pH dependence significantly. Upon a flash excitation, three components "fast proton release,""proton uptake" and "slow proton release" were observed at neutral pH in P77D. The pK(a) of PRC in the M intermediate was increased from 5.6 in the wild-type to 7.0, and became closer to that in AR4, which is 8.4. The coupling strength between D85 and PRC were also weakened, as expected. These data indicate that the 77th residue in AR4 greatly account for the difference between the two proton pumps.

摘要

野生型菌紫质（BR）和另一种视网膜蛋白嗜盐菌视紫红质 4（AR4）都是光驱动质子泵，但在中性 pH 下由于 AR4 中质子释放复合物（PRC）的更高 pK(a)，在闪光照射下质子释放和摄取的时间顺序相反。由于 BR 中细胞外侧的第 77 位残基是脯氨酸（P），而 AR4 中是天冬氨酸（D），因此我们在这项研究中用 D 突变了 BR 中的 P77。新的点突变被发现显著影响质子释放的动力学和 pH 依赖性。在中性 pH 下，在 P77D 中，在闪光激发后观察到三个组件“快速质子释放”、“质子摄取”和“慢速质子释放”。M 中间体中 PRC 的 pK(a)从野生型的 5.6 增加到 7.0，并且更接近 AR4 的 8.4，这是预期的。D85 和 PRC 之间的偶联强度也减弱了。这些数据表明，AR4 中的第 77 位残基极大地解释了这两种质子泵之间的差异。