Oxidative modification of the D1 residue 332H during photoinactivation drives photosystem II turnover.

Photosystem II (PS II) is a water-plastoquinone oxidoreductase. This photosystem has a short half-life (< 1 h) which is driven by repair of oxidative damage to the D1 protein. Reactive oxygen species (ROS) produced by the photosystem under stress conditions oxidatively modify key residues, which trigger the sequential disassembly of the photosystem. We hypothesize that the principal target for ROS damage of D1 is 332His. This residue is a ligand to Mn1 of the Mn4CaO5 cluster and is the first residue exhibiting oxidative modification during photoinactivation. Recently, cryo-EM studies indicate that PS II monomers containing oxidatively modified 332His lose their manganese clusters and the extrinsic proteins associated with the photosystem, both hallmarks of the earliest stages of PS II turnover/repair.