Pathways & interactions
Photosystem II cytochrome b559, alpha subunit, lumenal region (IPR013082)
Short name: PSII_cytb559_asu_lum
Overlapping homologous superfamilies
Oxygenic photosynthesis uses two multi-subunit photosystems (I and II) located in the cell membranes of cyanobacteria and in the thylakoid membranes of chloroplasts in plants and algae. Photosystem II (PSII) has a P680 reaction centre containing chlorophyll 'a' that uses light energy to carry out the oxidation (splitting) of water molecules, and to produce ATP via a proton pump. Photosystem I (PSI) has a P700 reaction centre containing chlorophyll that takes the electron and associated hydrogen donated from PSII to reduce NADP+ to NADPH. Both ATP and NADPH are subsequently used in the light-independent reactions to convert carbon dioxide to glucose using the hydrogen atom extracted from water by PSII, releasing oxygen as a by-product.
PSII is a multisubunit protein-pigment complex containing polypeptides both intrinsic and extrinsic to the photosynthetic membrane [PMID: 12518057, PMID: 15100025]. 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 10 kDa), and are involved in PSII assembly, stabilisation, dimerisation, and photo-protection [PMID: 14871485].
The alpha subunit (PsbE) of cytochrome b559, forms a haem-binding heterodimer with the beta subunit (PsbF) (IPR006241) within the reaction centre core of PSII. Both PsbE and PsbF are essential components for PSII assembly, and are probably involved in secondary electron transport mechanisms that help to protect PSII from photo-damage [PMID: 12560096].
This domain occurs in the lumenal region of the alpha subunit. It is usually found in conjuction with an N-terminal domain (IPR013081).
- PF00284 (Cytochrom_B559a)