Structural insights into photosystem II assembly

Nat Plants. 2021 Apr;7(4):524-538. doi: 10.1038/s41477-021-00895-0. Epub 2021 Apr 12.

Abstract

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 from Thermosynechococcus elongatus at 2.94 Å resolution. It contains three assembly factors (Psb27, Psb28 and 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 the bicarbonate ligand of non-haem iron with glutamate, a structural motif found in reaction centres of non-oxygenic photosynthetic bacteria. These results reveal 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.

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / ultrastructure
  • Photosynthesis
  • Photosystem II Protein Complex / genetics*
  • Photosystem II Protein Complex / ultrastructure
  • Thermosynechococcus / genetics
  • Thermosynechococcus / ultrastructure

Substances

  • Bacterial Proteins
  • Photosystem II Protein Complex

Supplementary concepts

  • Thermosynechococcus elongatus