7a4p
Structure of small high-light grown Chlorella ohadii photosystem I
Structural highlights
FunctionW8SY74_CHLSO PsaA and PsaB bind P700, the primary electron donor of photosystem I (PSI), as well as the electron acceptors A0, A1 and FX. PSI is a plastocyanin/cytochrome c6-ferredoxin oxidoreductase, converting photonic excitation into a charge separation, which transfers an electron from the donor P700 chlorophyll pair to the spectroscopically characterized acceptors A0, A1, FX, FA and FB in turn. Oxidized P700 is reduced on the lumenal side of the thylakoid membrane by plastocyanin or cytochrome c6.[ARBA:ARBA00002612][HAMAP-Rule:MF_00458] Publication Abstract from PubMedPhotosynthesis in deserts is challenging since it requires fast adaptation to rapid night-to-day changes, that is, from dawn's low light (LL) to extreme high light (HL) intensities during the daytime. To understand these adaptation mechanisms, we purified photosystem I (PSI) from Chlorella ohadii, a green alga that was isolated from a desert soil crust, and identified the essential functional and structural changes that enable the photosystem to perform photosynthesis under extreme high light conditions. The cryo-electron microscopy structures of PSI from cells grown under low light (PSI(LL)) and high light (PSI(HL)), obtained at 2.70 and 2.71 A, respectively, show that part of light-harvesting antenna complex I (LHCI) and the core complex subunit (PsaO) are eliminated from PSI(HL) to minimize the photodamage. An additional change is in the pigment composition and their number in LHCI(HL); about 50% of chlorophyll b is replaced by chlorophyll a. This leads to higher electron transfer rates in PSI(HL) and might enable C. ohadii PSI to act as a natural photosynthesiser in photobiocatalytic systems. PSI(HL) or PSI(LL) were attached to an electrode and their induced photocurrent was determined. To obtain photocurrents comparable with PSI(HL), 25 times the amount of PSI(LL) was required, demonstrating the high efficiency of PSI(HL). Hence, we suggest that C. ohadii PSI(HL) is an ideal candidate for the design of desert artificial photobiocatalytic systems. Cryo-EM photosystem I structure reveals adaptation mechanisms to extreme high light in Chlorella ohadii.,Caspy I, Neumann E, Fadeeva M, Liveanu V, Savitsky A, Frank A, Kalisman YL, Shkolnisky Y, Murik O, Treves H, Hartmann V, Nowaczyk MM, Schuhmann W, Rogner M, Willner I, Kaplan A, Schuster G, Nelson N, Lubitz W, Nechushtai R Nat Plants. 2021 Sep;7(9):1314-1322. doi: 10.1038/s41477-021-00983-1. Epub 2021 , Aug 30. PMID:34462576[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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