Brown L S, Needleman R, Lanyi J K
Department of Physiology and Biophysics, University of California, Irvine 92697, USA.
Biochemistry. 1999 May 25;38(21):6855-61. doi: 10.1021/bi990101d.
The functions of the four aspartic acid residues in interhelical loops at the cytoplasmic surface of bacteriorhodopsin, Asp-36, Asp-38, Asp-102, and Asp-104, were investigated by studying single and multiple aspartic acid to asparagine mutants. The same mutants were examined also with the additional D96N residue replacement. The kinetics of the M and N intermediates of the photochemical cycles of these recombinant proteins were affected only in a minor, although self-consistent, way. When residue 38 is an aspartate and anionic, it makes the internal proton exchange between the retinal Schiff base and Asp-96 about 3 times more rapid, and events associated with the reisomerization of retinal to all-trans about 3 times slower. Asp-36 has the opposite effect on these processes, but to a smaller extent. Asp-102 and Asp-104 have even less or none of these effects. Of the four aspartates, only Asp-36 could play a direct role in proton uptake at the cytoplasmic surface. In the 13 bacterioopsin sequences now available, only this surface aspartate is conserved.
通过研究单个和多个天冬氨酸突变为天冬酰胺的突变体，对细菌视紫红质细胞质表面螺旋间环中的四个天冬氨酸残基（Asp-36、Asp-38、Asp-102和Asp-104）的功能进行了研究。还对相同的突变体进行了额外的D96N残基替换检测。这些重组蛋白光化学循环中M和N中间体的动力学仅受到轻微影响，尽管是自洽的。当残基38为天冬氨酸且带负电时，它会使视黄醛席夫碱与Asp-96之间的内部质子交换速度加快约3倍，而与视黄醛异构化为全反式相关的事件则减慢约3倍。Asp-36对这些过程有相反的影响，但程度较小。Asp-102和Asp-104对这些过程的影响更小或没有影响。在这四个天冬氨酸中，只有Asp-36可能在细胞质表面的质子摄取中起直接作用。在目前可用的13个细菌视紫红质序列中，只有这个表面天冬氨酸是保守的。
