Post-Translational Events I Translocation of Newly Synthesized Proteins into Membranous Organelles

Locations of Protein Synthesis ER Associated Ribosomes –proteins translocate co-translationally into ER lumen –subsequent processing & transport through Golgi for secretory vesicles and lysosomes Cytoplasmic Ribosomes –proteins translocated post-translationally into membranous organelles (except Golgi, ER and lysosome)

Transport of Cytoplasmically Synthesized Proteins Import into organelles (transmembrane and lumenal) –Mitochondrial import –Chloroplast import –Peroxisome import Translocation across plasma membrane Insertion in cytoplasmic face of plasma membrane

Signal Sequences Portions of protein sequence –Frequently N-terminal, C-terminal –Occasionally located within –Often cleaved following transport event Signal Recognition Particles/Complexes –protein-translocation channels –escort (chaperone) proteins

Mitochondrial Protein Import Four Destinations –Outer membrane –Innermembranous space –Inner membrane –Matrix TOMs –Translocase of the outer mitochondrial membrane TIMs –Translocase of the inner mitochondrial membrane Tiny TIMs –escorts of the innermembranous space

TOM & TIM Function

Tiny TIMs and TIM22

TOC & TIC

Peroxisome Import Signal sequence for recognition by PEX5 -SKL- COOH

Peroxisome Formation

Translocation of ER-Associated Ribosome Synthesized Proteins

Docking of Ribosomes to ER Signal peptides typically residues – shorter than those on cytostolically synthesized proteins

Signal Recognition Particle Ribonucleoprotein complex Similar to bacterial SRP Ribosome binding Signal peptide binding translocation

Translocation of Various Classes of ER Proteins lumenal proteins Type 1 transmembrane proteins Type 2 transmembrane proteins multipass transmembrane proteins