How Does a Microbial Rhodopsin RxR Realize Its Exceptionally High Thermostability with the Proton-Pumping Function Being Retained?
Tomohiko Hayashi, Satoshi Yasuda, K. Suzuki, Tomoki Akiyama, Kanae Kanehara, Keiichi Kojima, Mikio Tanabe, Ryuichi Kato, Toshiya Senda, Yuki Sudo, Takeshi Murata, Masahiro Kinoshita
Abstract
atoms 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.