{"title":"D1-Tyr246 and D2-Tyr244 in photosystem II: Insights into bicarbonate binding and electron transfer from QA•− to QB","authors":"Ruri Nihara , Keisuke Saito , Hiroshi Kuroda , Yasuto Komatsu , Yang Chen , Hiroshi Ishikita , Yuichiro Takahashi","doi":"10.1016/j.bbabio.2024.149507","DOIUrl":null,"url":null,"abstract":"<div><p>In photosystem II (PSII), D1-Tyr246 and D2-Tyr244 are symmetrically located at the binding site of the bicarbonate ligand of the non-heme Fe complex. Here, we investigated the role of the symmetrically arranged tyrosine pair, D1-Tyr246 and D2-Tyr244, in the function of PSII, by generating four chloroplast mutants of PSII from <em>Chlamydomonas reinhardtii</em>: D1-Y246F, D1-Y246T, D2-Y244F, and D2-Y244T. The mutants exhibited altered photoautotrophic growth, reduced PSII protein accumulation, and impaired O<sub>2</sub>-evolving activity. Flash-induced fluorescence yield decay kinetics indicated a significant slowdown in electron transfer from Q<sub>A</sub><sup>•−</sup> to Q<sub>B</sub> in all mutants. Bicarbonate reconstitution resulted in enhanced O<sub>2</sub>-evolving activity, suggesting destabilization of bicarbonate binding in the mutants. Structural analyses based on a quantum mechanical/molecular mechanical approach identified the existence of a water channel that leads to incorporation of bulk water molecules and destabilization of the bicarbonate binding site. The water intake channels, crucial for bicarbonate stability, exhibited distinct paths in the mutants. These findings shed light on the essential role of the tyrosine pair in maintaining bicarbonate stability and facilitating efficient electron transfer in native PSII.</p></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149507"},"PeriodicalIF":3.4000,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Biochimica et Biophysica Acta-Bioenergetics","FirstCategoryId":"99","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0005272824004778","RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"BIOCHEMISTRY & MOLECULAR BIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
In photosystem II (PSII), D1-Tyr246 and D2-Tyr244 are symmetrically located at the binding site of the bicarbonate ligand of the non-heme Fe complex. Here, we investigated the role of the symmetrically arranged tyrosine pair, D1-Tyr246 and D2-Tyr244, in the function of PSII, by generating four chloroplast mutants of PSII from Chlamydomonas reinhardtii: D1-Y246F, D1-Y246T, D2-Y244F, and D2-Y244T. The mutants exhibited altered photoautotrophic growth, reduced PSII protein accumulation, and impaired O2-evolving activity. Flash-induced fluorescence yield decay kinetics indicated a significant slowdown in electron transfer from QA•− to QB in all mutants. Bicarbonate reconstitution resulted in enhanced O2-evolving activity, suggesting destabilization of bicarbonate binding in the mutants. Structural analyses based on a quantum mechanical/molecular mechanical approach identified the existence of a water channel that leads to incorporation of bulk water molecules and destabilization of the bicarbonate binding site. The water intake channels, crucial for bicarbonate stability, exhibited distinct paths in the mutants. These findings shed light on the essential role of the tyrosine pair in maintaining bicarbonate stability and facilitating efficient electron transfer in native PSII.
期刊介绍:
BBA Bioenergetics covers the area of biological membranes involved in energy transfer and conversion. In particular, it focuses on the structures obtained by X-ray crystallography and other approaches, and molecular mechanisms of the components of photosynthesis, mitochondrial and bacterial respiration, oxidative phosphorylation, motility and transport. It spans applications of structural biology, molecular modeling, spectroscopy and biophysics in these systems, through bioenergetic aspects of mitochondrial biology including biomedicine aspects of energy metabolism in mitochondrial disorders, neurodegenerative diseases like Parkinson''s and Alzheimer''s, aging, diabetes and even cancer.