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== Publication Abstract from PubMed ==

Roseiflexus castenholzii is a gram-negative filamentous phototrophic bacterium that carries out anoxygenic photosynthesis through a cyclic electron transport chain (ETC). The ETC is composed of a reaction center (RC)-light harvesting (LH) complex (rcRC-LH), an alternative complex III (rcACIII), which functionally replaces the cytochrome bc(1)/b(6)f complex, and the periplasmic electron acceptor auracyanin (rcAc). Although compositionally and structurally different from the bc(1)/b(6)f complex, rcACIII plays similar essential roles in oxidizing menaquinol and transferring electrons to the rcAc. However, rcACIII-mediated electron transfer (which includes both an intra-protein route and a downstream route) has not been clearly elucidated, nor have the details of cyclic ETC. Herein, we identified a previously unknown monoheme cytochrome c (cyt c(551)) as a novel periplasmic electron acceptor of rcACIII, it reduced the light-excited rcRC-LH to complete a cyclic ETC. We also revealed the molecular mechanisms involved in ETC using electron paramagnetic resonance (EPR), spectroelectrochemistry, enzymatic and structural analyses. We found that electrons released from rcACIII-oxidized menaquinol were transferred to two alternative periplasmic electron acceptors (rcAc and cyt c(551)), which eventually reduced the rcRC to form the complete cyclic ETC. This work serves as a foundation for further studies of ACIII-mediated electron transfer in anoxygenic photosynthesis, and broadens the understanding of the diversity and molecular evolution of the prokaryotic ETCs.

A cytochrome c(551) mediates the cyclic electron transport chain of anoxygenic phototrophic bacterium Roseiflexus castenholzii.,Yu L, Min Z, Liu M, Xin Y, Liu A, Kuang J, Wu W, JingyiWu, He H, Xin J, Blankenship RE, Tian C, Xu X Plant Commun. 2023 Sep 13:100715. doi: 10.1016/j.xplc.2023.100715. PMID:37710959<ref>PMID:37710959</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

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== References ==

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