post-translational events i translocation of newly synthesized proteins into membranous organelles
TRANSCRIPT
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 10-20 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