InterPro domain: IPR044900

PSII is a multisubunit protein-pigment complex containing polypeptides both intrinsic and extrinsic to the photosynthetic membrane [ 1 , 2 , 3 ]. Within the core of the complex, the chlorophyll and beta-carotene pigments are mainly bound to the antenna proteins CP43 (PsbC) and CP47 (PsbB), which pass the excitation energy on to the reaction centre proteins D1 (Qb, PsbA) and D2 (Qa, PsbD) that bind all the redox-active cofactors involved in the energy conversion process. The PSII oxygen-evolving complex (OEC) oxidises water to provide protons for use by PSI, and consists of OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ). The remaining subunits in PSII are of low molecular weight (less than 10kDa), and are involved in PSII assembly, stabilisation, dimerisation, and photo-protection [ 4 ].

This superfamily represents a domain found in the intrinsic antenna protein CP43 (PsbC), which is one of two such proteins found in the reaction centre of PSII, both of which can bind to chlorophyll 'a' and beta-carotene, passing the excitation energy on to the reaction centre [ 5 ]. It has a mainly alpha-helical structure.

1. Crystal structure of oxygen-evolving photosystem II from Thermosynechococcus vulcanus at 3.7-A resolution. Proc. Natl. Acad. Sci. U.S.A. 100, 98-103
2. The evolutionary development of the protein complement of photosystem 2. Biochim. Biophys. Acta 1655, 133-9
3. Thylakoid membrane lipid sulfoquinovosyl-diacylglycerol (SQDG) is required for full functioning of photosystem II in Thermosynechococcus elongatus. J Biol Chem 293, 14786-14797
4. The low molecular mass subunits of the photosynthetic supracomplex, photosystem II. Biochim. Biophys. Acta 1608, 75-96
5. Photosystem II: a multisubunit membrane protein that oxidises water. Curr. Opin. Struct. Biol. 12, 523-30