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BL3303 > Ubiquitination > Flashcards

Ubiquitination Flashcards

1
Q

What is the purpose of ubiquitination?

A
  • modify the location of components of the signalling pathways to different endomembranes, also in histone regulation
    2. Degradation and downregulation of a signalling pathway
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2
Q

How is a protein ubiquitinated?

A

Added post-translationally by ubiquitin ligase and removed by deubiquitinase

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3
Q

What is the strucutre of ubiquitin?

A
  • Large protein
  • 7 lysine residues (characteristic)
  • Attached by C-terminal glycine to form isopeptide bond with lysine on target amino acid
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4
Q

What are ubiquitin chains?

A
  • Many ubiquitin molecules attached by glycine-lysine isopeptide bond
    (polyubiquitination)
  • Can be extended or closed
  • Can be branched
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5
Q

Give examples of piolyubiquitin tails

A
  1. Lysine 63 is an extended linear chain which conforms non degredative roles
  2. Lysine 48 has a closed conformation, thought to be degredative
    (general rule of thumb but still not agreed in literature )
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6
Q

How do enzymes mediate ubiquitination?

A

Series of enzymatic reactions mediates by E1, E2 and E3

  • E1 enzymes activate monoubiquitin in an ATP dependent manner
  • E1 interacts with E2 and transfers ubiquitin via transthiolation reaction
  • E2 interacts with E3 mediating transfer on to target protein
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7
Q

What is the structure of E1?

A
  • Known as ubiquitin activating enzyme

- Conserved C-terminal cysteine which binds to ubiquitin in ATP dependent manner

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8
Q

What are the properties of E2?

A
  • Ubiquitin conjugating enzymes
  • Regulate which lysine chains are formed
  • Approximately 50 different types
  • Critical in determining substrate outcome
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9
Q

How do we know that cysteine is important for the functioning of E1 and E2?

A

Abolishing this abolishes ubiquitination

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10
Q

What are the properties of E3?

A
  • Ubiquitin ligase
  • 300 different types which mediate substrate binding
  • 3 families: HECT, RING and Ubox
    HETC - catalytic
    RING and ubox - non-catalytic
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11
Q

What are the properties of HETC E3?

A
  • Catalytic, ubiquitin transferred from E2 to E3 and then to substrate
  • Target protein binding N-terminal domain, C terminal HETC domain with conserved cysteine residue which recieves from E2
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12
Q

What are the properties of RING E3?

A
  • Make up 90% of ubiquitin ligases and are non-catalytic
  • Act as scaffold bringing substrate into close proximity but does not bind to E3
  • Cross-brace structure of cysteine and histidine residues linking central zinc residues
  • N terminal substrate binding domain can bind directly or through adaptor complexes
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13
Q

What are the 5 families of deubiquitinases?

A
  1. Ubiquitin C-terminal hydrolases (UCH) - hydrolyse bonds
  2. USP
  3. OUT
  4. Josephin domain
  5. JAMM
    (last 4 all proteases which cleave at lysine residues)
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14
Q

What are the functions of deubiquitinases?

A
  1. Processing ubiquitin monomeric subunits
  2. Editing chains
  3. Reverse ubiquitination
  4. Recycle ubiquitin from molecules that are to be degraded (ubiquitin is energetically expensive to produce)
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15
Q

What is the 26S proteosome?

A

Is the major system in which we can downregulate and degrade cytosolic based proteins

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16
Q

What are the two components of the 26S proteosome?

A

20S - has enzymatic activity which is degraded. Made from 4 layers of 7 subunits where the protease activity arises from the beta subunit, gating by alpha
19S - has 2 subunits (base and lid), contains 7 ATPases which mediate binding to 20S, provide energy to gate and helps unfold proteins

17
Q

What is the function of the lid in the 26S proteosome?

A

Unclear, however proteosome will not degrade ubiquitinated protein without it

18
Q

How is a protein degraded by the proteosome?

A
  • Protein binds to proteosome and is unwound by ATPases
  • Protein translocates through the pore once the gate is opened, being gradually degraded by protease activity by beta subunits
19
Q

What is the proposed interaction of protease with ubiquitin?

A
  • Ubiquitin interacts with lid domain where de-ubiquitinases are present
  • These work to remove ubiquitin while protein is degraded

BL3303 (15 decks)

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