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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 intraprotein route and a downstream route) has not been clearly elucidated, nor have the details of cyclic ETC. Here, we identify a previously unknown monoheme cytochrome c (cyt c(551)) as a novel periplasmic electron acceptor of rcACIII. It reduces the light-excited rcRC-LH to complete a cyclic ETC. We also reveal the molecular mechanisms involved in the ETC using electron paramagnetic resonance (EPR), spectroelectrochemistry, and enzymatic and structural analyses. We find that electrons released from rcACIII-oxidized menaquinol are transferred to two alternative periplasmic electron acceptors (rcAc and cyt c(551)), which eventually reduce 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 our understanding of the diversity and molecular evolution of prokaryotic ETCs.

A cytochrome c(551) mediates the cyclic electron transport chain of the anoxygenic phototrophic bacterium Roseiflexus castenholzii.,Yu L, Min Z, Liu M, Xin Y, Liu A, Kuang J, Wu W, Wu J, He H, Xin J, Blankenship RE, Tian C, Xu X Plant Commun. 2024 Feb 12;5(2):100715. doi: 10.1016/j.xplc.2023.100715. Epub 2023 , Sep 14. PMID:37710959^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.