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Biochem > Lecture 18: Protein processing and degradation > Flashcards

Lecture 18: Protein processing and degradation Flashcards

1
Q

Protein Export

A

-protein synthsis by ribosomes of rough ER
-lumen of ER like the exterior of cell
-signal peptide

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2
Q

Signal peptide

A

-usually at or near N-terminus
-positively charged N-terminal region and a core of 8-12 hydrophobic amino acids in a-helix
-followed by more polar C-terminal segement that serves as cleavage site

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3
Q

Protein export

A
  1. SRP recognizes signal peptide = STALLS translation
  2. SRP associates with SRP receptor
  3. ribosome associates with translocon
  4. translation resumes and peptides extrude into ER
    -signal cleaved by peptidase
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4
Q

Glycoproteins

A

-proteins with carb chains
-many exported proteins and extracellular domains of membrane proteins
-recognition signals

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5
Q

glycosylation

A

alters stablities, solubilities, and size of proteins

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6
Q

N-linked glycosylation

A

-oligosaccharide linked to amide nitrogen of asparagine in Asn-X-Thr sequence
-oligo is synthesized as intermediate with dolichol phosphate
-then transferred to new peptide in ER (cotranslational)

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7
Q

tunicamycin

A

-inhibits step A of N-linked glycosylation

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8
Q

glycosidases and glycosyltransferases

A

may further modify oligosaccharride

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9
Q

O-LINKED GLYCOSYLATION

A

-oligo bound to hydroxyl of serine/theronine
-occurs in golgi (posttranslational)
-initiated by GalNAc-transferase
-results in heterogenous oligos

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10
Q

Targeting to membranes

A
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11
Q

anchoring sequence

A

-hydrophobic
-inserted to the membranes through TRANSLOCON
-multiple sequence = protein spans membrane multiple times

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12
Q

Retention of SOLUBLE proteins in ER

A

-C-terminal KDEL sequence

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13
Q

Targeting to nucleus

A

-made in cytosol with nuclear localization signals (clusters of amino acids)
-PKKKRKV
-KR[PAATKKAGQA]KKKK
-transported by carrier proteins to nuclear pore complexes
-needs GTPase Ran
-phosphorylation of SPS or TPT seq includes nuclear uptake

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14
Q

Targeting to mitochondira

A

-made in cytosol as PREproteins with N-terminal presequences (+ charged helices)
-recognized by mitochondrial receptor
-TOM and TIM complex
-translocation requires unfolding
-energy DEPENDENT

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15
Q

TOM

A

-translocase of outer membrane

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16
Q

TIM

A

-translocase of inner membrane

17
Q

protein turnover

A

-constant
-regulate metabolism
-eliminate bad proteins
-break down as carbon and nitrogen sources in time of need

18
Q

protein half lives

A

-short for regulatory
-long for housekeeping

19
Q

Lyosomal protein degradation

A

-contain ~50 hydrolytic enzymes
-ph 5
-cathepsins

20
Q

lysosomal uptake

A

-endocytosis for extracellular
-autophagy for intracellular (nonselective)

21
Q

Protein degradation

A

-to amino acids
-recycled for protein synthesis or metabolized
-proteolysis

22
Q

Intracellular proteolysis

A

-POLYUBIQUINATION marks protein for degradation
-PROTEASOMEs recognize polyubiquinated proteins
-proteins unfolded and translocated into chamber of proteasomes USING ATP
-Proteasome active site inside chamber

23
Q

Ubiquitin dependent protein degradation

A

-highly conserved
-posttranslational mod
-E1-E3

24
Q

E1

A

-activates ubiquitin to form thioester withits C-term
-ATP REQUIRED

25
Q

E2

A

-transfers activated ubiquitin to substrate protein

26
Q

E3

A

catalyzes ligation between lysine of protein and C-term of ubiquitin
-SPECIFIC for protein

27
Q

ATP-dependent unfolding

A
  1. recognition of polyubiquitin chain
  2. Translocation of substrate chain
  3. Deubiquination
  4. Unfolding
  5. Proteolysis
28
Q

Regulation of protein degradation

A

-N-end rule
-ERAD

29
Q

N-end rule

A

-N-term of amino acid determines lifetime
-Arg 1 hour
-Val 100 hour
-part of ubiquintin degradation
-not sole regulator

30
Q

ER-associated degradation (ERAD)

A

-misfold proteins in ER moved back to cytosol
-protein polyubiquinated during translocation
-proteasomes in cytosol degrade polyubiquinated proteins

31
Q

MDM2

A

-regulate p53
-E3 ligase
-expressed by p53
-suppress p53 activity
-p53 is low under normal conditions

32
Q

regulation of p53

A

-MDM2
-phosphorylation
-E6

33
Q

Phosphorylation of p53 upon DNA damage

A

-activates p53 by blocking MDM2 binding
-supresses degradation

34
Q

E6 in HPV

A

-brings p53 to E6AP (E3 ligase)
-induces degradation by ubiquination
-blocks apoptosis

Biochem (30 decks)

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