BIOLOGY 2D03 Lecture Notes - Endosome, Oligosaccharide, Consensus Sequence

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28 Jan 2013
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CHAPERONES, QUALITY CONTROL, TURNOVER
CHAPERONES: bind to and facilitate the correct FATE of another protein
chaperone binding can affect:
folding
assembly
compartmentalization
degradation
**do not accelerate correct folding, but DECELERATE incorrect folding**
differentiates chaperones from isomerases (folding proteins)
also known as HSP’s – (heat shock proteins)
upregulated during heat shock (to prevent misfolding)
bind newly translated peptides off the ribosome prevents aggregation
involved in mitochondrial transport (easier when protein is unfolded)
HSP70 binding cycle: PREVENTS AGGREGATION
1. low affinity binding (hydrophobic stretch recognition) “open”
2. ATP hydrolysis high affinity binding “closed”
3. ADP removed chaperone disassociates
HSP60: double doughnut structure
very large (1/2 size of ribosome)
central cavity provides shielded environment for folding
“protein shield”
also ATPase activity
HSP70 binding tends to precede HSP60 folding
HSP 90: conformational maturation of steroid hormone receptors and signaling
kinases
**aggregation can cause disease by inducing conformational changes**
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TURNOVER: misfolded proteins must be eliminated
Regulation: compartmentalization
selective activation
turnover is studied by pulse (5 minutes)-chase (hours); half-lives determined
LIPID DEGRADATION:
glycerophospholipids can be degraded/remodeled throughout the cell
sphingolipids – centralized degradation (lysosome)
cholesterol – not degraded; its levels are regulated by controlling synthesis
PROTEIN DEGRADATION
- disposal of damaged proteins
- metabolic control
- cell differentiation
- cell cycle / proliferation control
- antigen presentation
PROTEASOME – cytosolic degradation (as opposed to intra-organelle)
PROTEASOME SYSTEM:
30% of newly made proteins fail to fold properly!!
4 concentric rings + 2 caps (for regulation)
complete proteasome = 26S
inner rings (B-chains) contain proteolytic activity
narrow entrance can’t insert folded proteins
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