Cryo-EM photosystem I structure reveals adaptation mechanisms to extreme high light in Chlorella ohadii

Ido Caspy, Ehud Neumann, Maria Fadeeva, Varda Liveanu, Anton Savitsky, Anna Frank, Yael Levi Kalisman, Yoel Shkolnisky, Omer Murik, Haim Treves, Volker Hartmann, Marc M. Nowaczyk, Wolfgang Schuhmann, Matthias Rögner, Itamar Willner, Aaron Kaplan, Gadi Schuster, Nathan Nelson, Wolfgang Lubitz, Rachel Nechushtai

Research output: Contribution to journalArticlepeer-review

Abstract

Photosynthesis 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 (PSILL) and high light (PSIHL), obtained at 2.70 and 2.71 Å, respectively, show that part of light-harvesting antenna complex I (LHCI) and the core complex subunit (PsaO) are eliminated from PSIHL to minimize the photodamage. An additional change is in the pigment composition and their number in LHCIHL; about 50% of chlorophyll b is replaced by chlorophyll a. This leads to higher electron transfer rates in PSIHL and might enable C. ohadii PSI to act as a natural photosynthesiser in photobiocatalytic systems. PSIHL or PSILL were attached to an electrode and their induced photocurrent was determined. To obtain photocurrents comparable with PSIHL, 25 times the amount of PSILL was required, demonstrating the high efficiency of PSIHL. Hence, we suggest that C. ohadii PSIHL is an ideal candidate for the design of desert artificial photobiocatalytic systems.

Original languageEnglish
Pages (from-to)1314-1322
Number of pages9
JournalNature Plants
Volume7
Issue number9
DOIs
StatePublished - Sep 2021

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