InterPro: IPR003210 Signal recognition particle, SRP14 subunit

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 [1, 2]. SRP recognises the signal sequence of the nascent polypeptide on the ribosome, retards its elongation, and docks the SRP-ribosome-polypeptide complex to the RER membrane via the SR receptor. 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 [3]. 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.

This entry represents the 14 kDa SRP14 component. Both SRP9 and SRP14 have the same (beta)-alpha-beta(3)-alpha fold. The heterodimer has pseudo two-fold symmetry and is saddle-like, consisting of a curved six-stranded beta-sheet that has four helices packed on the convex side and an exposed concave surface lined with positively charged residues. The SRP9/SRP14 heterodimer is essential for SRP RNA binding, mediating the pausing of synthesis of ribosome associated nascent polypeptides that have been engaged by the targeting domain of SRP [4].