How Does a Microbial Rhodopsin RxR Realize Its Exceptionally High Thermostability with the Proton-Pumping Function Being Retained?
How Does a Microbial Rhodopsin RxR Realize Its Exceptionally High Thermostability with the Proton-Pumping Function Being Retained?
复制标题
微生物视紫红质 RxR 如何在保留质子泵浦功能的情况下实现极高的热稳定性？
DOI：
10.1021/acs.jpcb.9b10700
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Kinoshita Masahiro
中科院分区：
文献类型：
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作者：
Hayashi Tomohiko;Yasuda Satoshi;Suzuki Kano;Akiyama Tomoki;Kanehara Kanae;Kojima Keiichi;Tanabe Mikio;Kato Ryuichi;Senda Toshiya;Sudo Yuki;Murata Takeshi;Kinoshita Masahiro
我们经常会遇到这样一种情况，两种氨基酸序列相似的蛋白质在热稳定性方面有很大的不同。作为一个引人注目的例子，我们考虑了两个七跨膜蛋白：最近发现的木质红杆菌视紫红质(RXR)和从盐生杆菌中长期已知的细菌视紫红质(HsBR)。它们通常作为光驱动的质子泵穿过膜起作用。虽然它们的序列相似性和同源性分别为∼71和∼45%，但RXR的热稳定性比HsBR高得多。在这项研究中，我们用X射线结晶学解决了RXR的三维结构，发现RXR和HsBR的主链结构惊人地相似：用七个螺旋的主链C-α原子计算两种结构的均方根偏差只有0.86o，这使得巨大的稳定性差异更加令人费解。我们用我们最近发展的统计力学理论计算了RXR和HsBR的热稳定性测量及其能量和熵分量。对于在质子泵功能中起关键作用的螺旋3和7，同样的计算是独立进行的，它们的结构性质与水分子在质子传输机制中的可能作用有关。我们成功地阐明了RXR是如何在保留原有功能的情况下实现其异常高的稳定性的。这项研究为建立一种将蛋白质的微观几何特征与其热力学性质相关联并通过氨基酸突变增强热稳定性而不破坏原有功能的方法提供了重要的第一步。
We often encounter a case where two proteins, whose amino-acid sequences are similar, are quite different with regard to the thermostability. As a striking example, we consider the two seven-transmembrane proteins: recently discoveredRubrobacter xylanophilusrhodopsin (RxR) and long-known bacteriorhodopsin fromHalobacterium salinarum(HsBR). They commonly function as a light-driven proton pump across the membrane. Though their sequence similarity and identity are ∼71 and ∼45%, respectively, RxR is much more thermostable than HsBR. In this study, we solve the three-dimensional structure of RxR using X-ray crystallography and find that the backbone structures of RxR and HsBR are surprisingly similar to each other: The root-mean-square deviation for the two structures calculated using the backbone Cαatoms of the seven helices is only 0.86 Å, which makes the large stability difference more puzzling. We calculate the thermostability measure and its energetic and entropic components for RxR and HsBR using our recently developed statistical-mechanical theory. The same type of calculation is independently performed for the portions playing essential roles in the proton-pumping function, helices 3 and 7, and their structural properties are related to the probable roles of water molecules in the proton-transporting mechanism. We succeed in elucidating how RxR realizes its exceptionally high stability with the original function being retained. This study provides an important first step toward the establishment of a method correlating microscopic, geometric characteristics of a protein with its thermodynamic properties and enhancing the thermostability through amino-acid mutations without vitiating the original function.