Photosystem I PsaA/PsaB (IPR001280)

Short name: PSI_PsaA/B

Overlapping homologous superfamilies

Family relationships


Photosystem I (PSI) [PMID: 3333014] is an integral membrane protein complex that uses light energy to mediate electron transfer from plastocyanin to ferredoxin. PSI is found in the chloroplast of plants and cyanobacteria. The electron transfer components of the reaction centre of PSI are a primary electron donor P-700 (chlorophyll dimer) and five electron acceptors: A0 (chlorophyll), A1 (a phylloquinone) and three 4Fe-4S iron-sulphur centres: Fx, Fa, and Fb.

PsaA and psaB, two closely related proteins, are involved in the binding of P700, A0, A1, and Fx. psaA and psaB are both integral membrane proteins of 730 to 750 amino acids that seem to contain 11 transmembrane segments. The Fx 4Fe-4S iron-sulphur centre is bound by four cysteines; two of these cysteines are provided by the psaA protein and the two others by psaB. The two cysteines in both proteins are proximal and located in a loop between the ninth and tenth transmembrane segments. A leucine zipper motif seems to be present [PMID: 2186925] downstream of the cysteines and could contribute to dimerisation of psaA/psaB.

GO terms

Biological Process

GO:0015979 photosynthesis

Molecular Function

No terms assigned in this category.

Cellular Component

GO:0016021 integral component of membrane
GO:0009522 photosystem I
GO:0009579 thylakoid

Contributing signatures

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