Topic 1.5 Protein Signals Used to Sort Proteins to Their Destinations
Co-translational and Post-translational Sorting Signals for Proteins
Organelle |
Function of signal |
Protein signal sequence |
Receptor for signal |
ER |
Cotranslational insertion of protein |
N-terminal hydrophobic domain of 6-12 AA |
Signal Recognition Particle |
ER |
Maintains protein in the ER |
C-terminal Lys-Asp-Glu-Leu |
HDEL- Receptor or ERD2 |
Golgi |
Maintains trans-membrane protein in the Golgi |
Trans-membrane domain |
Unknown |
Vacuole |
Targets endomembrane protein to vacuole |
N-terminal Asn-Pro-Ile-Arg |
BP80 or VSR-At1 |
Vacuole |
Targets endomembrane protein to vacuole |
C-terminal with hydrophobic stretches |
RMR (for receptor homology-transmembrane-RING H2 domains) |
Peroxisome |
Posttranslational insertion of protein |
C-Terminal Ser-Lys-Leu |
SKL receptor |
Mitochondrion |
Posttranslational insertion of protein |
Amphipathic (helical, with positive charge on one side, negative charge on the other) sequence |
Outer membrane transporter – TOM22/TIM 17 complex |
Chloroplast |
Posttranslational insertion of protein |
No consensus sequence |
Outer membrane transporter – TOC159 and other polypeptides |
Chloroplast |
Cotranslational insertion in ER followed by transfer to chloroplast at adhesion sites |
N-terminal hydrophobic domain for ER targeting, unknown domain for association with chloroplast (example: Carbonic anhydrase 1) |
ER signal recognition system and unknown system in the chloroplast |
Nucleus |
Targets transcription factors, histones, and other proteins to the nucleus |
Examples: |
Importin component of the nuclear pore |