Protein targeting signal recognition particle

Qi, H.-Y., and Bernstein, H. (1999). SecAis required for the insertion of inner membrane proteins targeted by the Eschericha coli signal recognition particle. J. Biol. Chem. 274, 8993-8997. 

Proteins are targeted to various locations after synthesis by signal sequences. Thus, proteins destined for the ER, the mitochondria and chloroplasts have particular kinds of signal sequences at the N-terminus. ER-targeted proteins enter the ER directly off rough ER ribosomes via a signal recognition particle (SRP) complex that is linked to an SRP receptor and a ribosome receptor-transmembrane peptide translocation complex associated with the ER membrane. Within, the ER polypeptides are processed and folded and S—S links are formed. 

A targeting chaperone involved in the transmembrane transport of proteins involves the recognition of the signal peptide. See Pool, M.R, Signal recognition particles in chloroplasts, bacteria, yeast, and mammals. Mol. Membrane Biol. 22, 3-15, 2004. 

A small RNA molecule is an essential component of the signal-recognition particle, an RNA protein complex in the cytoplasm that helps target newly synthesized proteins to intracellular compartments and extracellular destinations. 

In cotranslational translocation, the signal-recognition particle (SRP) first recognizes and binds the ER signal sequence on a nascent secretory protein and in turn is bound by an SRP receptor on the ER membrane, thereby targeting the ribosome/nascent chain complex to the ER. 

Protein translocation across the ER membrane involves the interaction between ribosomes and the signal recognition particle (SRP). SRP is thought to recognize a signal sequence in the nascent protein which causes it to bind tightly to the active ribosome (1,2). This in turn provokes translational arrest, followed by the targeting of the dormant ribosome/SRP complex to the SRP receptor in the ER membrane. 

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