Anomalous pH Effect of Blue Proteorhodopsin

作者：Yamada Keisuke; Kawanabe Akira; Yoshizawa Susumu; Inoue Kentaro; Kogure Kazuhiro; Kandori Hideki^*

来源：Journal of Physical Chemistry Letters, 2012, 3(7): 800-804.

DOI：10.1021/jz3000257

Proteorhodopsin (PR) is a light-driven proton pump found in marine bacteria, and thousands of PRs are classified into blue-absorbing PR (B-PR; lambda(max) approximate to 490 nm) and green-absorbing PR (G-PR; lambda(max) approximate to 525 nm). In this report, we present conversion of B-PR into G-PR using anomalous pH effect B-PR in LC1-200, marine gamma-proteobacteria, absorbs 497 and 513 nm maximally at pH 7 and 4, respectively, whose pH titration was reversible (pK(a) = 4.8). When pH was lowered from 4, the lambda(max) was further red-shifted (528 nm at pH 2). This is unusual because blue shift occurs by chloride binding in the case of bacteriorhodopsin. Surprisingly, when pH was increased from 2 to 7, the lambda(max) of this B-PR was further red-shifted to 540 nm, indicating that green-absorbing PR (PR540) is created only by changing pH. The present study reports the conformational flexibility of microbial rhodopsins, leading to the switch of absorbing color by a simple pH change.

• 出版日期2012-4-5