Homologous Superfamily

Signal recognition particle, SRP54 subunit, M-domain superfamily (IPR036891)

Short name: Signal_recog_part_SRP54_M_sf

Overlapping entries


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].

This entry represents the M domain superfamily of the 54kDa SRP54 component, a GTP-binding protein that interacts with the signal sequence when it emerges from the ribosome. SRP54 of the signal recognition particle has a three-domain structure: an N-terminal helical bundle domain, a GTPase domain, and the M-domain that binds the 7s RNA and also binds the signal sequence. The extreme C-terminal region is glycine-rich and lower in complexity and poorly conserved between species.

These proteins include Escherichia coli and Bacillus subtilis ffh protein (P48), which seems to be the prokaryotic counterpart of SRP54; signal recognition particle receptor alpha subunit (docking protein), an integral membrane GTP-binding protein which ensures, in conjunction with SRP, the correct targeting of nascent secretory proteins to the endoplasmic reticulum membrane; bacterial FtsY protein, which is believed to play a similar role to that of the docking protein in eukaryotes; the pilA protein from Neisseria gonorrhoeae, the homologue of ftsY; and bacterial flagellar biosynthesis protein flhF.

GO terms

Biological Process

GO:0006614 SRP-dependent cotranslational protein targeting to membrane

Molecular Function

GO:0008312 7S RNA binding

Cellular Component

GO:0048500 signal recognition particle

Contributing signatures

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