Illustration showing a ribosome (blue) presenting a newly synthesised polypeptide (orange) to a Sec61 protein (green) in the membrane of the endoplasmic reticulum (ER). Attached to the polypeptide is a ribonucleo-complex signal recognition particle (SRP, purple), which binds to a SRP receptor (pink) on Sec61 and displaces the plug (bright green) that blocks the channel. This allows the peptide to enter the lumen of the ER where it will be modified and packaged for onward transport. Mutations and overexpression of Sec61 have been linked to a number of diseases including diabetes and cancers, making the Sec61 complex a target for therapeutic drugs.