Photosystem II PsbY (IPR009388)

Short name: PSII_PsbY

Overlapping homologous superfamilies


Family 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].

This family represents the low molecular weight transmembrane protein PsbY found in PSII. In higher plants, two related PsbY proteins exist, PsbY-1 and PsbY-2, which appear to function as a heterodimer. In spinach and Arabidopsis, these two proteins arise from a single-copy nuclear gene that is processed in the chloroplast. By contrast, prokaryotic and organellar chromosomes encode a single PsbY protein, as found in cyanobacteria and red algae, indicating a duplication event in the evolution of higher plants [PMID: 15042356]. PsbY has two low manganese-dependent activities: a catalase-like activity and an L-arginine metabolising activity that converts L-arginine into ornithine and urea [PMID: 9829828]. In addition, a redox-active group is thought to be present in the protein. In cyanobacteria, PsbY deletion mutants have a slightly impaired PSII that is less capable of coping with low levels of calcium ions than the wild-type.

GO terms

Biological Process

GO:0015979 photosynthesis

Molecular Function

GO:0030145 manganese ion binding

Cellular Component

GO:0016021 integral component of membrane
GO:0009523 photosystem II

Contributing signatures

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