Signal recognition particle receptor, alpha subunit homologue, N-terminal (IPR015284)

Short name: Sig_recog_part_rcpt_asu-like_N

Domain relationships

  • Longin-like domain (IPR011012)
    • Signal recognition particle receptor, alpha subunit homologue, N-terminal (IPR015284)


The signal recognition particle (SRP) is a multimeric protein, which along with its conjugate receptor (SR), is involved in targeting secretory proteins to the rough endoplasmic reticulum (RER) membrane in eukaryotes, or to the plasma membrane in prokaryotes [PMID: 17622352, PMID: 16469117]. SRP recognises the signal sequence of the nascent polypeptide on the ribosome. In eukaryotes this retards its elongation until SRP docks the ribosome-polypeptide complex to the RER membrane via the SR receptor [PMID: 12605305]. Eukaryotic SRP consists of six polypeptides (SRP9, SRP14, SRP19, SRP54, SRP68 and SRP72) and a single 300 nucleotide 7S RNA molecule. The RNA component catalyses the interaction of SRP with its SR receptor [PMID: 17507650]. In higher eukaryotes, the SRP complex consists of the Alu domain and the S domain linked by the SRP RNA. The Alu domain consists of a heterodimer of SRP9 and SRP14 bound to the 5' and 3' terminal sequences of SRP RNA. This domain is necessary for retarding the elongation of the nascent polypeptide chain, which gives SRP time to dock the ribosome-polypeptide complex to the RER membrane. In archaea, the SRP complex contains 7S RNA like its eukaryotic counterpart, yet only includes two of the six protein subunits found in the eukarytic complex: SRP19 and SRP54 [PMID: 12364595].

The SR receptor is a monomer consisting of the loosely membrane-associated SR-alpha homologue FtsY, while the eukaryotic SR receptor is a heterodimer of SR-alpha (70 kDa) and SR-beta (25 kDa), both of which contain a GTP-binding domain [PMID: 12654246]. SR-alpha regulates the targeting of SRP-ribosome-nascent polypeptide complexes to the translocon [PMID: 10859309]. SR-alpha binds to the SRP54 subunit of the SRP complex. The SR-beta subunit is a transmembrane GTPase that anchors the SR-alpha subunit (a peripheral membrane GTPase) to the ER membrane [PMID: 7844142]. SR-beta interacts with the N-terminal SRX-domain of SR-alpha, which is not present in the bacterial FtsY homologue. SR-beta also functions in recruiting the SRP-nascent polypeptide to the protein-conducting channel.

This entry represents a homologue of the alpha subunit of the SR receptor. Members of this entry consist of a central six-stranded anti-parallel beta-sheet sandwiched by helix alpha1 on one side and helices alpha2-alpha4 on the other. They interact with the small GTPase SR-beta, forming a complex that matches a class of small G protein-effector complexes, including Rap-Raf, Ras-PI3K(gamma), Ras-RalGDS, and Arl2-PDE(delta) [PMID: 12654246].

Contributing signatures

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