Topic 1.5 Protein Signals Used to Sort Proteins to Their Destinations

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:
Import: Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
Export: Leu-Ala-Leu-Lys-Leu-Ala-Gly-Leu-Asp-Ile

Importin component of the nuclear pore