Signal Recognition Particle Receptor (SRPR)

The signal recognition particle receptor, also termed 'docking protein,' is an integral membrane protein of the endoplasmic reticulum (ER). Interaction of the SRPR with the signal recognition particle (SRP) on the arrested ribosome is essential for the protein targeting process in the ER membrane. SRP recognizes the signal sequences of nascent secretory proteins and arrests the elongation of the polypeptide chain, thus preventing completion of the presecretory protein. SRP54 is positioned at the exit site close to ribosomal proteins L23a and L35. When SRP54 contacts the SRPR, SRP54 is rearranged such that it is no longer close to L23a. This repositioning may allow the translocon to dock with the ribosome, leading to insertion of the signal peptide into the translocation channel.