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Protein Folding - Coggle Diagram
Protein Folding
Eukaryotes
Co-translational
SRPs bind signal sequence of nascent protein as it emerges from the ribosome
Stall protein synthesis by blocking exit tunnel and the A-site on the ribosome
Deliver ribosome with nascent protein to the sec61 complex on the ER membrane.
SRP dissociates and signal sequence is recognised by the sec61 complex
Other proteins such as TRAP and OST facilitate recognition and translocation of the protein
Sec61 complex contains a large RNA component which indicates that it is an ancient particle
Membrane protein insertion
Different mechanisms employed depending on which side the N and C termini have to be
EMC shown to be required for membrane insertion
Post-translational (yeast and probably higher eukaryotes)
Nascent protein emerges from ribosome and is kept unfolded by chaperones which deliver it to the Sec61/62/63 complex on the ER membrane.
Signal sequence is recognised by membrane complex and translocated from the cytosol into the ER lumen
interaction between ATP bound BiP and the J domain of sec63 facilitates ATP hydrolysis.
ADP bound BiP binds to nascent protein strand and prevents backsliding of the polypeptide into the cytosol
Once all of the polypeptide chain has been translocated nucleotide exchange on BiP leads to dissociation from protein
Organelle transport
Mitochondria
TOM on outer membrane
TIM 23 to be translocated into matrix or inner membrane
Tim 22 translocates beta barrels into inner membrane
proteins from within translocated to inner membrane by Oxa1
Chloroplast
Toc
Tac
Stroma
SponL, cpSRP, cpSec and cpTat
into thylakoid lumen and membrane
Outer and inner membranes
Nucleus
Not much known
Prokaryotes