Lecture 12 Flashcards
where does most protein synthesis in a eukaryotic cell start
free cytosolic ribosomes except mt and plastid translation
what are chaperonins
provide a cage that isolates small (<70 kDa) folding proteins from the cytosol. residence time = 10s
how is the fate of a chaperone client proteins detemined
concentration of Hsc70 and Hsp90 co chaperones
HOP
transfers clients froom Hsc70 to Hsp90
BAG-1
releases Hsc70 clients at the proteasome, favouring destruction
BAG-2
releases clients away from the proteasome, favours folding
HIP
competes with NEFs, maintains the Hsc70:client interaction
what are the 4 things cytosolic molecular chaperones do?
- prevent aggregation of unfolded proteins
- provide a controlled environment for folding
- permit assembly of multimeric complexes
- direct proteins with folding problems for destruction
what are they 3 proteolytic activities the 20s core particles have?
trypsin-like
chymotrypsin-like
peptidylglutamyl-peptide hydrolysing
What are 6 other cytosolic post-translational modifications
- proteolytic cleavage to activate a protein e.g. procaspase 3 is stored in an inactive condition.
- addition of lipids to permit membrane targeting e.g. Rabs are
- phosphorylation - control of CDK activation, p53
- ADP ribosylation - addition of 1/more ADP-ribose molecules and ADP-ribosylated proteins have roles in cell signalling, DNA repair and apoptosis
- methylation - typically takes place of lysine or argenine residues in the proteins
