Ubiquitin & The Proteasome Flashcards
proteasome structure
20S core + 2 19S lids; not found in mitochondria, ER, or Golgi
physiological roles for proteasome
destruction of misfolded/oxidized proteins, cell cycle control, transcription, signal transduction, and antigen presentation
20S core
4 stacked rings made of 7 proteins each; 2 alpha rings on outside and 2 beta rings in middle; 3/7 inner ring subunits have proteolytic activity (beta1, beta2, beta5)
19S regulatory particle
made of lid and base; lid selects ubiquitinate substrates and removes ubiquitin to hand off to base; base openes pore of core by using its AAA + ATPase
ubiquitylation
-COOH terminus of ubiquitin is attached to lysine residue of substrate protein via isopeptide bond
ubiquitylation steps
E1 adenylates ubiquitin (attaches AMP to Ub) –> transfers it to thiol group on active site, cleaving AMP –> transfers it to E2 –> E3 can bring E2 to substrate, allowing transfer of Ub to Lys or E3 can have an active site and Ub can be transferred to E3 and then the protein
substrate for E2/E3
epsilon-amino group of protein substrate Lys, epsilon-amino group of ubiquitin lysine, or alpha-amino group of N-terminal methionine of Ub
Which lysines will be poly-ubiquitinated?
K11 and K48 leading to degradation
E3 recognizes
PEST, destruction box, ken box, and N-end rule
de-ubiquitylation
DUBs hydrolyze isopeptide bond between C-terminus of Ub and lysine to recycle Ub
rate limiting step for proteasomal degradation
K-48 poly-ubiquitination
p27 regulation
inhibitor of cyclin–> stable in cell until its phosphorylated –> once its phosphorylated, it’s a phospho-degron –> recognized by E3
mitotic cyclin regulation
stable until E3 is phosphorylated –> degraded
HIF-1
induces genes necessary for oxygenated blood (like at high altitudes, hypoxic conditions)
HIF-1 regulation
HIF-1a is prolyl hydroxylated –> active degron –> degraded by E3 (VHL)
-if reduce oxygen conditions in cell, HIF-1a can not get prolyl-hydroxylated
Von-Hippel Lindau syndrome
people who lack VHL –> accumulate benign tumors
p53 regulation
E3 MDM2 causes ubiquitylation of p53 –> cell cycle can not be repressed –> tumors
cdk/cyclin E regulation
if SCF is repressed, it will not bind E3 for degradation of cyclin E –> cdk is continuously bound to cyclin E –> cell cycle always on
ERAD mechanism
incorrectly folded protein will be ubiquitylated once it hits cytoplasmic face –> Cdc48/P97 (AAA + ATPase will bind) –> extract protein from ER –> present to proteasome for degradation
multiple myeloma
hyper active ERAD and UPR, proteasome inhibitors will kill cells
examples of proteasome inhibitors
Bortezomib and Carfilzomib
