Intracellular proteolysis Flashcards
Understand: - Mechanisms of proteolytic processes. - Mechanisms of action behind statins.
Serine proteases [3 marks]
- Have a very reactive serine residue in their active sites
- Examples: thrombin, chymotrypsin
- Serine residue has OH
Aspartyl proteases [2 marks]
- Have a very reactive aspartate residue in their active sites
- Example: HIV I protease
Bromelain and papain [2 marks]
- Involved in meat tenderisers
- Digest collagen and other proteins to make meats easier to chew
Aspartyl proteases [2 marks]
- Have a very reactive aspartate residue in their active sites
- Example: HIV I protease
HIV I protease [3 marks]
- Cleaves polypeortein precursors to Gag and Pol proteins
- This helps makes new virions, which need to be processed for proteolysis
- This enzyme is blocked by anti-retroviral drugs
What are gag proteins? [1 mark]
- Group specific antigens
What are pol proteins? [1 mark]
Code for enzymes such as reverse transcriptase and HIV protease
Metalloproteases [2 marks]
- Uses metal ions to catalyse proteolysis
- Two types; endopeptidase and exopeptidase
Endopeptidase [1 mark]
Cleaves off protein within sequence
Exopeptidase [2 mark]
- Enzymes that cleave off single amino acid at the end
- Either from amino terminus or from the carboxyl terminus
Specific proteases [2 marks]
- Recognises specific amino acid sequence
- Involved in protein activation (i.e. insulin)
Non-specific proteases [1 mark]
Involved in protein degradation (i.e. proteases in small intestine)
Synonyms for an inactive protein [2 marks]
- Zymogen
- Proprotein
α-Chymotrypsin synthesis [3 marks]
- Chymotrypsinogen is cleaved between position 6 and 7 to form π-Chymotrypsin
- Autolysis of π-Chymotrypsin at position 13 and 16 and position 146 and 149 to form α-Chymotrypsin
- Two depeptides are released from π-Chymotrypsin
Trypsin synthesis [2 marks]
- Trypsinogen is cleaved off between position 6 and 7 to form trypsin
- Enzyme used is enteropeptidase
What is needed for intron removal? [2 marks]
- Specific sequences at splice donor and splice acceptor
- Needs an AG in front of the next exon
Deficiency of factor IX (X linked haemophilia) cause and effect [4 marks]
- Mutation creates a new splice acceptor
- Exon starts with different nucleotide sequence
- Reading frame shift creates a new amino acid sequence and abrupt stop codon
- Blood cannot coagulate properly
Ubiquitin [2 marks]
- Covalently attached to proteins
- Guides protein to proteasome (26S proteasome)
Ubiquitin activating enzyme 1 (E1) [2 marks]
- Formation of thioester bond between C end of ubiquitin and cysteine in E1.
- Requires ATP
Ubiquitin activating enzyme 2 (E2) [1 mark]
Transfer of ubiquitin to a cysteine on E2
Ubiquitin activating enzyme 3 (E3) [2 marks]
- Transfer of ubiquitin from E2 to lysine on the target protein
- Many different E3 exist that recognise specific target proteins
Stabilising residue [2 marks]
- U3 ubiquitin ligases have a low affinity to them
- Degradation of these proteins are slower
Destabilising residue [2 marks]
U3 ubiquitin ligases have a high affinity to them
- Degradation is faster
How do statins work? [3 marks]
- Block cholesterol synthesis via inhibition of HMG CoA reductase
- Acts like a competitive inhibitor
- Increases uptake of LDL through LDL receptor
What is the sterol regulatory element binding protein (SREBP)? [2 marks]
- A transcription factor
- Regulates gene for enzymes
SREBP action in low cholesterol [2 marks]
- Binds to promotor of LDL receptor proteins
- Goes to nucleus and activates genes for cholesterol supply
What happens in low cholesterol? [4 marks]
- Insig and SCAP dissociate
- Causes SCAP to reverse its conormational shape
- In the Golgi, SREBP is activated via proteolysis to form N-SREBP (N terminus cleaved off)
- N-SREBP released from the Golgi
What is the purpose of N-SREBP? [1 mark]
Goes to the nucleus to activate cholesterol synthesis proteins
What happens in high cholesterol? [4 marks]
- SREBP is synthesised because proteins with transmembrane remains
- It is anchored in the membrane of the endoplasmic reticulum and remains there.
- Forms a complex with SCAP to cause a conformational change
- This allows SCAP to bind to Insig.
