Rapid-Scan Fourier Transform Infrared Monitoring of the Photoactivation Process in Cyanobacterial Photosystem II

Takumi Matsubara; Yuichiro Shimada; Tomomi Kitajima-Ihara; Ryo Nagao; Takumi Noguchi

doi:10.1021/acs.jpcb.3c04325

Rapid-Scan Fourier Transform Infrared Monitoring of the Photoactivation Process in Cyanobacterial Photosystem II

J Phys Chem B. 2023 Sep 28;127(38):8150-8161. doi: 10.1021/acs.jpcb.3c04325. Epub 2023 Sep 17.

Authors

Takumi Matsubara¹, Yuichiro Shimada¹, Tomomi Kitajima-Ihara¹, Ryo Nagao², Takumi Noguchi¹

Affiliations

¹ Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan.
² Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan.

PMID: 37718495
DOI: 10.1021/acs.jpcb.3c04325

Abstract

The catalytic site of photosynthetic water oxidation, the Mn₄CaO₅ cluster, in photosystem II (PSII) is known to be formed by a light-induced process called photoactivation. However, details of its molecular mechanism remain unresolved. In this study, we monitored the photoactivation process in cyanobacterial PSII using rapid-scan, time-resolved Fourier transform infrared (FTIR) spectroscopy. The Mn³⁺/Mn²⁺ FTIR difference spectra of PSII, in which D1-D170 was specifically ¹³C labeled, and PSII from the D1-D170A, D1-E189A, and D1-D342A mutants provide strong evidence that the initial Mn²⁺ is coordinated by D1-D170 and D1-E189. Protein conformational changes and relocation of photo-oxidized Mn³⁺ in the dark rearrangement process were detected as slow-phase signals in the amide I and carboxylate regions, whereas similar signals were not observed in D1-E189A PSII. It is thus proposed that relocation of Mn³⁺ via D1-E189 induces the conformational changes of the proteins to form proper Mn binding sites in the mature protein conformation.