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Cellular Biology and Biochemistry > Proteolysis - Latency and Activation > Flashcards

Proteolysis - Latency and Activation Flashcards

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1
Q

What are pre-peptides?

A

Signal peptides responsible in translocation and translation through membranes

Secretory proteins which are synthesised with signal peptides at the N-terminus which is removed after sorting by proteolysis

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2
Q

What are Pro-peptides?

A

Folding intramolecular chaperones.

These must be removed for activity to occur.

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3
Q

How does latency relate to the secretory pathway?

A

Most bioactive polypeptides must be inactive whilst in the secretory pathway and then become activated when they are released.
(proteins synthesised in an inactive form)

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4
Q

What does the Trans-Golgi network do?

A

Sorting of protein and membrane components to constitutive and regulated pathways and to lysosomes.

Cleavage of some pro-proteins also occurs.

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5
Q

What is a secretagogues?

A

A substance that causes another substance to be secreted.

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6
Q

Where does the constitutive pathways deliver its components to?

A

The plasma membrane

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7
Q

Where does the regulated pathway deliver its components to?

A

Forma pool of contents awaiting a secretagogues for release into the cells

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8
Q

What is essential for activation of a protein?

A

Pro-peptide cleavage.

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9
Q

What do cleavage sites contain?

A

At least 2 basic residues

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10
Q

What removes the 2 basic residues in cleavage sites after cleavage?

A

Carboxypeptidase

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11
Q

What are PCSKs?

A

Proprotein Convertases Subtilisin/Kexin (prohormone converting enzymes)

They are serine proteases and so will cleave at these sites on pro-peptides.

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12
Q

How were PCSKs found?

A

Found by homology with Kex 2 from yeast.

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13
Q

What was the first mammalian PCSK found and how many are there in total?

A

First found was Furin (PCSK3)

Currently 9 known mammalian PCSKs

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14
Q

What are the general structure of PCSK genes?

A

Signal peptide
Prosegment (synthesised in inactive forms)
catalytic domain
P-domain

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15
Q

What is required for PCSK activation?

A

Synthesised with a prosegment which requires autocatalytic cleavage to activate the PCSK.

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16
Q

What is the role of the P-domain in the PCSK gene?

A

Regulates the activity of the catalytic domain

Reacts to pH and ion concentration changes.

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17
Q

What do PCSK specifically cleave?

A

Cleave mostly C-terminal to arg

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18
Q

What amino acids are recognised by PCSKs?

A

Arg/Lys

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19
Q

What dictates PCSK specificity?

A

Dictated by a sequence 2-5 amino acids N-terminal to the bond cleaved.

20
Q

What is the preference cleavage site for PCSK1,2,3?

A

PCSK1 -RR (arg, arg)

PCSK2 - KR (Lys, Arg)

PCSK3 - RXKR (Arg, Any AA, Lys, Arg)

21
Q

What PCSKs are found in the secretory pathway?

A

PCSK1 and 2

22
Q

What PCSKs are found in the constitutive pathway?

A

PCSK 3, 5, 6, 9

23
Q

What are the transmembrane PCSKs?

A

PCSK 3, 5, 7

24
Q

What is special about PCSK3?

A

Recycles through the plasma membrane and endosomal compartments

25
Q

What are the important roles for PCSKs?

A

Pro-peptide cleavage

Protein maturation - Insulin

Receptor recycling - LDL

Exploitation by pathogens - toxin activation

26
Q

What is the role of PCSK in pro-peptide cleavage?

A

Provide control for mature protein production

Allow tissue-specific expression of peptide hormones
from common precursors.

27
Q

What is the role of PCSK in insulin maturation?

A

Synthesised as preproinsulin (pre is cleaved after synthesis)

Proinsulin is inactive precursor.

Processing by PCSK2 and then PCSK1 to yield mature insulin within the regulated secretory vesicle

28
Q

What is the role of PCSK9 in LDL receptor recycling?

A

Role in LDL cholesterol metabolism
Promotes LDL receptor degradation in the lysosome
Prevents LDLR recycling to the plasma membrane
Reduces LDLR number at the plasma membrane
Reduces clearance of LDL from circulation

29
Q

What can PCSK9 be used to treat?

A

Hypercholesterolaemia

30
Q

What do viruses exploit PCSKs for?

A

For the maturation of envelope glycoproteins

potential therapeutic target

31
Q

What is the role of PCSK3 in toxin activation in bacteria and plants?

A

These species contain PCSK3 cleavage sites.
A chain acts as a pro-peptide targeting the toxin to the membrane
PCSK3 cleaves the A chain and liberates the B chain.
B chain can cross the secretory pathway membrane and inactivate ribosomes

32
Q

What cleavage events occur at the cell surface?

A

Matrix metalloproteinases act on the ECM

Secretases liberate active domains from membrane bound proteins

33
Q

What are the roles matrix metalloproteinases?

A

Cell surface cleavage

Role in cancer invasion

34
Q

What are the important roles in secretases?

A

Cell surface activation of proteins

Role in Alzheimer’s

35
Q

How are matrix metalloproteinases activated?

A

Activated by Zinc

36
Q

What is the purpose of the cystine switch in the pro domain of the matrix metalloproteinases?

A

During the folding, the cystine inhibits the catalytic activity of the metalloproteinases and therefore requires cleavage of the pro form to release the cystine residue and activate the protein.

37
Q

What is the importance of the modification of the structure of the ECM by matrix metalloproteinases?

A

Proliferation
Apoptosis
Morphogenesis

38
Q

What are the roles of metalloproteinases in prostate cancer?

A

A prostate tumour cell synthesises pro-MMPs which can then be activated when zin is present. This means the MMP can degrade the ECM and allow for cell migration and metastasis

39
Q

What are the secretases?

A

Alpha - redundant group of ADAM9, 10, 17

Beta - BACE aspartyl protease

Gamma - presenilins

40
Q

What are the roles of alpha secretases?

A

2 domain proteases
Active at or close to the cell surface
Responsible for a wide range of sheddase activities

41
Q

Give an example of a molecule that ADAM proteases activates?

A

EGF activation

42
Q

What is APP?

A

Amyloid precursor protein

43
Q

What is Alzheimer’s disease characterised by?

A

Formation of amyloid plaques in the brain by secretases.

44
Q

What is the role of APP?

A

Expressed in neuronal and extra-neuronal tissues and have roles in adhesion, migration and gene expression

45
Q

How are amyloid plaques formed?

A

Beta and gamma secretases produce Abeta plaques so inhibition of secretases cause be a therapeutic use of Alzheimer’s disease.

Cellular Biology and Biochemistry (22 decks)

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