Mechanism of SP recognition and ER docking
1. Signal peptide is first recognized by SRP in the cytosol, which pauses translation
2. SRP then targets the ribosome-nascent chain complex to the ER membrane by binding to the SRP receptor
3. This interaction guides the ribosome to the ER translocon, a channel through which the nascent protein enters the ER lumen
4. Upon docking, SRP is released and recycled, and the translocon opens to allow the protein to enter the ER