title: Photosynthetic system in Blastochloris viridis revisited.
abstract: The bacterium Blastochloris viridis carries one of the simplest photosynthetic systems, which includes a single light-harvesting complex that surrounds the reaction center, membrane soluble quinones, and a soluble periplasmic protein cytochrome c(2) that shuttle between the reaction center and the bc(1) complex and act as electron carriers, as well as the ATP synthase. The close arrangement of the photosynthetic membranes in Bl. viridis, along with the extremely tight arrangement of the photosystems within these membranes, raises a fundamental question about the diffusion of the electron carriers. To address this issue, we analyzed the structure and response of the Bl. viridis photosynthetic system to various light conditions, by using a combination of electron microscopy, whole-cell cryotomography, and spectroscopic methods. We demonstrate that in response to high light intensities, the ratio of both cytochrome c(2) and bc(1) complexes to the reaction centers is increased. The shorter membrane stacks, along with the notion that the bc(1) complex is located at the highly curved edges of these stacks, result in a smaller average distance between the reaction centers and the bc(1) complexes, leading to shorter pathways of cytochrome c(2) between the two complexes. Under anaerobic conditions, the slow diffusion rate is further mitigated by keeping most of the quinone pool reduced, resulting in a concentration gradient of quinols that allows for a constant supply of theses electron carriers to the bc(1) complex.
authors.affiliation: Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel. marina.konorty@weizmann.ac.il
authors.forename: Marina
authors.initials: M
authors.lastname: Konorty
authors.forename: Vlad
authors.initials: V
authors.lastname: Brumfeld
authors.forename: Andre
authors.initials: A
authors.lastname: Vermeglio
authors.forename: Nava
authors.initials: N
authors.lastname: Kahana
authors.forename: Ohad
authors.initials: O
authors.lastname: Medalia
authors.forename: Abraham
authors.initials: A
authors.lastname: Minsky
mesh_terms: D000222:Adaptation, Physiological; D025243:Bacterial Proton-Translocating ATPases / Q000737:chemistry / Q000648:ultrastructure; D004058:Diffusion; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry / Q000648:ultrastructure; D005470:Fluorometry; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000648:ultrastructure; D012241:Rhodopseudomonas / Q000737:chemistry* / Q000201:enzymology / Q000254:growth & development / Q000648:ultrastructure; D020524:Thylakoids / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D025243:Bacterial Proton-Translocating ATPases; D014450:Electron Transport Complex III