Microscopic basis of reaction center modulation in PsbA variants of photosystem II

• 成果类型: Article
• 署名作者: Bhattacharjee, Sinjini; Gordiy, Igor; Sirohiwal, Abhishek; Pantazis, Dimitrios A.
• 署名单位: Max Planck Society; Indian Institute of Science (IISC) - Bangalore
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13822
• DOI: 10.1073/pnas.2417963122
• 发表日期: 2025-05-20
• 关键词: primary charge separation; primary electron-acceptor; photosynthetic reaction centers; time-resolved fluorescence; thermosynechococcus-elongatus; wild-type; extrinsic proteins; gene-expression; distinct forms; quantum yield

摘要

Photosystem II (PSII) is a protein-pigment complex that utilizes sunlight to catalyze water oxidation and plastoquinone reduction, initiating the electron transfer (ET) cascade in oxygenic photosynthesis. The D1 and D2 proteins are the most important transmembrane subunits of PSII that bind all redox-active components involved in primary charge separation (CS) and ET. D1 is susceptible to oxidative photodamage, particularly under high light, and protection partly involves genetic regulation. Cyanobacterial D1 is encoded by the psbA gene family that expresses distinct isoforms (PsbA1-3) depending on environmental conditions. Most differences in D1 isoforms are close to the active-branch reaction center (RC) pigments PD1, PD2, ChlD1, and PheoD1. Here, we combine molecular dynamics simulations with multiscale quantum-mechanics/molecular-mechanics calculations on the membrane-bound PSII monomer of each variant to compare the redox and excited state properties of RC pigments using long-range-corrected density functional theory. We identify specific amino acid substitutions responsible for electrochromic shifts on distinct pigments and pigment groups. Our results indicate that the PheoD1 acceptor is the primary regulatory target. The redox properties of the ChlD1-PheoD1 pair and the energetics of ChlD1 delta+PheoD1 delta- charge-transfer states are distinctly modulated in the three isoforms: Compared to the standard psbA1, charge separation is inhibited in psbA2 and facilitated in psbA3 PSII. The results provide a microscopic description of how genetic variations modulate protein electrostatics and influence primary processes in photosynthetic reaction centers.