proteolysis Flashcards
what do proteases, proteinases, peptidases and cathepsins do?
enzymes that cleave peptide bonds
what are cathepsins?
lysosomal proteins
why do proteases in the small intestine need to be non specific?
so they can degrade any type of protein that is ingested
what is a proprotein?
the precursor of the active form
how does chymotrypsin get activated?
trypsin cleaves amino acids from chymotrypsinogen and it becomes active chymotrypsin, and three amino acids are removed so three separate peptide chains are made which are joined by disulfide bonds.
what is the activation of factor 12 in the clotting cascade activated by?
damaged surfaces
how does HIV-1 protease work?
HIV genome produces two proteins called Gag and Pol that need to be processed by proteolysis. HIV-1 cleaves these two proteins and activate them.
What are the two pathways for protein degradation?
Lysosomal degradation and the other is the ubiquitin proteasome pathway
What are ubiquitins?
small regulatory proteins that are attached covalently to the substrate protein.
What is the proteasome?
a large protease complex the active sites all point towards the center of the inner cavity.
How many peptides is ubiquitin made from?
76
what does ubiquitin do?
acts like a marker for proteins that need to be broken down.
what does formation of the isopeptide bond require?
ATP
describe ubiquitylation
1) ACTIVATION: formation of a thioester bond between the COOH terminus of ubiquitin and a cysteine in E1 (requires ATP)
2) CONJUGATION: transfer of ubiquitin from cysteine onto E2
3) LIGATION: transfer of ubiquitin from E2 to a lysine in the target protein, or to the other ubiquitin molecules already attached to a target (polyubiquitination)
How many ubiquitin molecules need to be added to the bound ubiquitin?
4