Secretory proteins include many hormones, enzymes, toxins, and antimicrobial peptides.
The part that is produced first, the N-terminal, contains a signal sequence consisting of 6 to 12 amino acids with hydrophobic side chains.
This sequence is recognised by a cytosolic protein, SRP (Signal Recognition Particle), which stops the translation and aids in the transport of the mRNA-ribosome complex to an SRP receptor found in the membrane of the endoplasmic reticulum.
The signal sequence is removed and the translation continues while the produced chain moves through the translocon (cotranslational translocation).
The process has been extended to the host–pathogen interface, wherein, gram negative bacteria secrete outer membrane vesicles containing fully conformed signal proteins and virulence factors via exocytosis of nano-sized vesicles, in order to control host or target cell activities and exploit their environment.