How to build a water-splitting machine: structural insights into photosystem II assembly
Marc Nowaczyk a
a Ruhr University Bochum, Germany, Universitätsstraße, 150, Bochum, Germany
Proceedings of International Online Conference on Bio-hybrid Approaches to Solar Energy Conversion (Biohybrid)
Online, Spain, 2020 October 27th - 29th
Organizers: Jenny Zhang, Vincent Friebe and Lars Jeuken
Contributed talk, Marc Nowaczyk, presentation 021
Publication date: 8th October 2020

Biogenesis of photosystem II (PSII), nature’s water splitting catalyst, is assisted by auxiliary proteins that form transient complexes with PSII components to facilitate stepwise assembly events. Using cryo-electron microscopy, we solved the structure of such a PSII assembly intermediate with 2.94 Å resolution. It contains three assembly factors (Psb27, Psb28, Psb34) and provides detailed insights into their molecular function. Binding of Psb28 induces large conformational changes at the PSII acceptor side, which distort the binding pocket of the mobile quinone (QB) and replace bicarbonate with glutamate as a ligand of the non-heme iron, a structural motif found in reaction centers of non-oxygenic photosynthetic bacteria. These results reveal novel mechanisms that protect PSII from damage during biogenesis until water splitting is activated. Our structure further demonstrates how the PSII active site is prepared for the incorporation of the Mn4CaO5 cluster, which performs the unique water splitting reaction. [1]

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