Protein targeting signal sequence secretory

The majority of proteins to be targeted to the secretory route are initially synthesized as precursors containing a hydrophobic signal being either a cleav-able N-terminal peptide [9] or a noncleavable internal sequence located near the N-terminus [10]. Signal peptides of some proteins have been shown to mediate efficient secretion in heterologous environments. 

A Hydrophobic N-Terminal Signal Sequence Targets Nascent Secretory Proteins to the ER... 

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. 

In post-translational translocation, a completed secretory protein is targeted to the ER membrane by interaction of the signal sequence with the translocon. The polypeptide chain is then pulled into the ER by a ratcheting mechanism that requires ATP hydrolysis by the chaperone BiP, which stabilizes the entering polypeptide (see Figure 16-9). 

Type I Proteins All type I transmembrane proteins possess an N-terminal signal sequence that targets them to the ER and an internal hydrophobic sequence that becomes the membrane-spanning a helix. The N-termlnal signal sequence on a nascent type I protein, like that of a secretory protein,... 

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