The Psb32 protein aids in repairing photodamaged photosystem II in the cyanobacterium Synechocystis 6803.

Photosystem II (PSII), a membrane protein complex, catalyzes the photochemical oxidation of water to molecular oxygen. This enzyme complex consists of approximately 20 stoichiometric protein components. However, due to the highly energetic reactions it catalyzes as part of its normal activity, PSII is continuously damaged and repaired. With advances in protein detection technologies, an increasing number of sub-stoichiometric PSII proteins have been identified, many of which aid in the biogenesis and assembly of this protein complex. Psb32 (Sll1390) has previously been identified as a protein associated with highly active purified PSII preparations from the cyanobacterium Synechocystis sp. PCC 6803. To investigate its function, the subcellular localization of Psb32 and the impact of deletion of the psb32 gene on PSII were analyzed. Here, we show that Psb32 is an integral membrane protein, primarily located in the thylakoid membranes. Although not required for cell viability, Psb32 protects cells from oxidative stress and additionally confers a selective fitness advantage in mixed culture experiments. Specifically, Psb32 protects PSII from photodamage and accelerates its repair. Thus, the data suggest that Psb32 plays an important role in minimizing the effect of photoinhibition on PSII.