Intracellular Proteolysis Flashcards
What is proteolysis?
It is the breakdown of proteins into amino acids using enzymes.
What are endopeptidases?
Enzymes which break peptide bonds other than terminal ones in a peptide chain- it cleaves off via the inside of the peptide.
What are exopeptidases?
Enzymes which cleave off the terminal peptide bonds, either on the N-terminus or C-terminus.
What are aminopeptidases?
Enzymes which catalyse the cleavage of amino acids from the amino terminus (N-terminus) of proteins.
What are carboxypeptidases?
Enzymes that hydrolyse a peptide bond at the carboxy-terminus (C-terminus) of proteins.
What is protein activation?
The process where inactive proteinases become activated via cleavaging .
How are stomach enzymes activated? (Trypsinogen, Trypsin)
Trypsinogen is a inactive precursor of trypsins which is a an enzyme that is generated in the stomach to aid digestion.
An enzyme called enteropeptidase is an enzyme which cleaves trypsinogen between the positions 6 and 7 to create its active form, trypsin.
How is chymotrypsin created?
Chymotrypsinogen is cleaved by trypsin to create π-chymotrypsin. This then cleaves itself via autolysis which generates active α-chymotrypsin.
What is an example of a serine protease?
Formation of blood clots form an amplifying cascade of different Serine proteases
Queen Victoria was a carrier of haemophilia and passed it on to many of the royal family descendants.
She had a mutation in a serine protease called factor IX – this prevents clotting and causes bleeding
Deficiencies of Factor VIII or IX are the Cause of X-Linked Haemophilia.
The gene is on the X-chromosomes so only males are affected, very rare among females, however, females can be carriers.
Scientists sequenced factor IX gene and found a mutation in intron between exon 3 and exon 4
‘A’ is lost and this defect is very close to the splice acceptor site so because of this mutation the intron is not spliced out.
So protein doesn’t continue with next exon and starts a new reading frame which quickly leads to a stop codon.
Therefore protein no longer formed.
What is an example of cysteine protease?
Bromelain, Papain (enzymes) are very commonly used as meat tenderizer
Papain is isolated from papaya plant
Bromelain is isolated from bromeliad
Proteases are useful as meat tenderisers because they break down the extracellular matrix proteins (because they are quite accessible and they hold the structure of the muscles together – therefore meat is a lot easier to chew if they are broken)
What is an example of aspartyl protease?
An example of a aspartyl protease includes the HIV-1 Protease (AKA retropepsin).
HIV is the virus that causes AIDS and people discovered that the AIDS virus generates proteins that had to be proteolytically processed to generate key proteins that the virus needs to replicate and in order to assemble new viral particles.
So if you block that protease (HIV-1 Protease) with a drug you might be able to treat AIDS more effectively.
After isolating and identifying the protease it was possible to determine the 3D structure, and based on the structure were able to design a small drug inhibitor using enzyme assays.
Patients receive a cocktail of inhibitor of protease and other enzymes
This lead to a drastic reduction in Number of deaths (in thousands) from AIDS after production of protein inhibitor in 1995.
How is the compartment formed for non-specific protein degradation?
Compartment is formed through the formation of an organelle that has its own membrane – that shield the proteases from the other proteins in the cell.
What are the ways that degradation in cells are compartmentalised?
Lysosomes have a very low pH (proton conc.1000 times higher than cytoplasm) so if enzymes escaped from lysosomes they wouldn’t be active because pH in cytoplasm is a lot higher
Ubiquitination of proteins targets which are then taken to a structure in cells called proteasome
-This is a compartment that is not formed by
membranes it’s a complex of proteinases involved in
breaking down selected intracellular proteins.
-It has a cylindrical form that has a cavity in middle
that shields any substrates that get in there
-Active site of proteases that face into the centre of
cylinder are shielding the rest of the cell from this
protease.
-Proteins are degraded, AA and ubiquitin are
released and recycled.
How is the 3D structure of a proteasome created and what shape does it show?
It is created using crystallography and the image shows a bell shape of a proteasome.
What do proteins have to go through in order for it to be able enter a proteasome?
The protein has to be ubiquitinated which is a process where a small protein called ubiquin is attached to the protein. Ubiquitination is highly regulated and require three different enzymes.
