Multiple retinal isomerizations during the early phase of the bestrhodopsin photoreaction

• 成果类型: Article
• 署名作者: Kaziannis, Spyridon; Broser, Matthias; Stokkum, Ivo H. M. van; Dostal, Jakub; Busse, Wayne; Munhoven, Arno; Bernardo, Cesar; Kloz, Miroslav; Hegemann, Peter; Kennis, John T. M.
• 署名单位: University of Ioannina; Humboldt University of Berlin; Vrije Universiteit Amsterdam
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-14449
• DOI: 10.1073/pnas.2318996121
• 发表日期: 2024-03-19
• 关键词: stimulated raman-spectroscopy; ion-pump rhodopsin; all-trans; vibrational analysis; structural-changes; bacteriorhodopsin; light; photoisomerization; chromophore; photochemistry

摘要

Bestrhodopsins constitute a class of light- regulated pentameric ion channels that consist of one or two rhodopsins in tandem fused with bestrophin ion channel domains. Here, we report on the isomerization dynamics in the rhodopsin tandem domains of Phaeocystis antarctica bestrhodopsin, which binds all - trans retinal Schiff - base (RSB) absorbing at 661 nm and, upon illumination, converts to the meta- stable P540 state with an unusual 11 - cis RSB. The primary photoproduct P682 corresponds to a mixture of highly distorted 11 - cis and 13 - cis RSB directly formed from the excited state in 1.4 ps. P673 evolves from P682 in 500 ps and contains highly distorted 13 - cis RSB, indicating that the 11 - cis fraction in P682 converts to 13 - cis. Next, P673 establishes an equilibrium with P595 in 1.2 mu s, during which RSB converts to 11 - cis and then further proceeds to P560 in 48 mu s and P540 in 1.0 ms while remaining 11 - cis. Hence, extensive isomeric switching occurs on the early ground state potential energy surface (PES) on the hundreds of ps to mu s timescale before finally settling on a metastable 11 - cis photoproduct. We propose that P682 and P673 are trapped high up on the ground - state PES after passing through either of two closely located conical intersections that result in 11 - cis and 13 - cis RSB. Co- rotation of C11=C12 and C13=C14 bonds results in a constricted conformational landscape that allows thermal switching between 11 - cis and 13 - cis species of highly strained RSB chromophores. Protein relaxation may release RSB strain, allowing it to evolve to a stable 11 - cis isomeric configuration in microseconds. Significance The far - red absorbing rhodopsin modules (Amax = 661 nm) of bestrhodopsin are of high interest for a principle understanding of the photophysics and photochemistry of unusually far - red absorbing rhodopsins and optogenetic application in tissues that are more transparent to red light in comparison to blue or green light. Moreover, the identified light- induced isomeric switching processes on the ground state potential energy surface disclose a multiisomerization activation mechanism that has so far remained unknown for rhodopsin.