Chen Min, Sawicki Artur, Wang Fanyue
School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia.
Microorganisms. 2023 Sep 13;11(9):2305. doi: 10.3390/microorganisms11092305.
Photosystem II (PSII) is a quinone-utilizing photosynthetic system that converts light energy into chemical energy and catalyzes water splitting. PsbA (D1) and PsbD (D2) are the core subunits of the reaction center that provide most of the ligands to redox-active cofactors and exhibit photooxidoreductase activities that convert quinone and water into quinol and dioxygen. The performed analysis explored the putative uncoupled electron transfer pathways surrounding P induced by far-red light (FRL) based on photosystem II (PSII) complexes containing substituted D1 subunits in . Chlorophyll -synthase (ChlF) is a D1 protein paralog. Modeling PSII-ChlF complexes determined several key protein motifs of ChlF. The PSII complexes included a dysfunctional MnCaO cluster where ChlF replaced the D1 protein. We propose the mechanism of chlorophyll synthesis from chlorophyll via free radical chemistry in an oxygenated environment created by over-excited pheophytin and an inactive water splitting reaction owing to an uncoupled MnCaO cluster in PSII-ChlF complexes. The role of ChlF in the formation of an inactive PSII reaction center is under debate, and putative mechanisms of chlorophyll biosynthesis are discussed.
光系统II（PSII）是一种利用醌的光合系统，可将光能转化为化学能并催化水的分解。PsbA（D1）和PsbD（D2）是反应中心的核心亚基，它们为氧化还原活性辅因子提供大部分配体，并表现出光氧化还原酶活性，可将醌和水转化为对苯二酚和二氧。所进行的分析基于含有取代D1亚基的光系统II（PSII）复合物，探索了远红光（FRL）诱导的围绕P的假定非耦合电子转移途径。叶绿素合酶（ChlF）是一种D1蛋白旁系同源物。对PSII-ChlF复合物进行建模确定了ChlF的几个关键蛋白基序。PSII复合物包括一个功能失调的MnCaO簇，其中ChlF取代了D1蛋白。我们提出了在PSII-ChlF复合物中由过度激发的脱镁叶绿素和由于未耦合的MnCaO簇导致的无活性水分解反应所产生的氧化环境中，通过自由基化学从叶绿素合成叶绿素的机制。ChlF在无活性PSII反应中心形成中的作用仍在争论中，并且讨论了叶绿素生物合成的假定机制。
