PsbP, C-terminal (IPR002683)

Short name: PsbP_C

Overlapping homologous superfamilies

Domain relationships



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].

In PSII, the oxygen-evolving complex (OEC) is responsible for catalysing the splitting of water to O(2) and 4H+. The OEC is composed of a cluster of manganese, calcium and chloride ions bound to extrinsic proteins. In cyanobacteria there are five extrinsic proteins in OEC (PsbO, PsbP-like, PsbQ-like, PsbU and PsbV), while in plants there are only three (PsbO, PsbP and PsbQ), PsbU and PsbV having been lost during the evolution of green plants [PMID: 15258264].

This entry represents the C-terminal domain found in PSII OEC protein PsbP. Both PsbP and PsbQ (IPR008797) are regulators that are necessary for the biogenesis of optically active PSII. PsbP increases the affinity of the water oxidation site for chloride ions and provides the conditions required for high affinity binding of calcium ions [PMID: 9039496, PMID: 8910540]. The crystal structure of PsbP from Nicotiana tabacum (Common tobacco) revealed a two-domain structure, where domain 1 may play a role in the ion retention activity in PSII, the N-terminal residues being essential for calcium and chloride ion retention activity [PMID: 15031714]. PsbP is encoded in the nuclear genome in plants.

GO terms

Biological Process

GO:0015979 photosynthesis

Molecular Function

GO:0005509 calcium ion binding

Cellular Component

GO:0019898 extrinsic component of membrane
GO:0009523 photosystem II
GO:0009654 photosystem II oxygen evolving complex

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.