Crystal structure analysis of extrinsic PsbP protein of photosystem II reveals a manganese-induced conformational change.

The Mn cluster (Mn4CaO5) on the thylakoid luminal side of photosystem II (PSII) catalyzes the photosynthetic oxygen-evolving reaction, an essential process for life on Earth. In higher plants and green algae, the Mn cluster is surrounded by the membrane-extrinsic proteins PsbO (33 kDa), PsbP (23 kDa), and PsbQ (17 kDa) (Murata and Miyao, 1985). They shield the Mn cluster, protecting and stabilizing it from attack by exogenous reductants. PsbP plays an indispensable role in PSII function, and is necessary for the retention of Ca2+ and Cl– (Ghanotakis et al., 1984), the assembly of PSII complex (Yi et al., 2007), and the maintenance of normal thylakoid architecture (Yi et al., 2009).