Lecture 18 Sjogren Flashcards
Molecular Chaperones
assist the covalent folding or unfolding of proteins
assembly or disassembly of macromolecular structures (oligomerization or aggregates)
Examples of Chaperones
HSP60 - GroEL/GroES
HSP70 - DnaK
HSP90 - HtpG
Disorders in Chaperones
affect muscle, bone, and CNS
Problematic Chaperones
partially folded or misfolded proteins are bad –> aggregation
- exposure of the hydrophobic residues and unstructured polypeptide backbone
- aggregation results in amorphous structures
Overview of Proteasome Complexity through PTM
Genome (20-25,000 genes) –> Alternative promoters and alternative splicing –> Transcriptome (100,000 transcripts) –> PTM –> Proteome (1,000,000 proteins)
PTM Functions
Proteolytic Processing & Conformational Change –> Activation
PTM-dependent proteolysis –> Degradation
PTM-dependent recognition –> Activation, interaction, localization, and secretion
Reversible-site PTM –> Dynamic regulation or modulation
Purpose of Protein Degradation
misfolded proteins
dietary proteins to supplement amino acids
regulation of cellular processses
Protein Degradation Overview
Controls:
- blood clotting
- processing pro forms of proteins
- cell matrix proteolysis
- replication and transcription
Eliminates:
- misfolded or unfolded proteins
- damage proteins
- large aggregates (cause Alzeheimer, Parkinson, Huntington, ALS)
Protein Degradation Processes
Ubiquitin Proteolysis
- proteins that are targeted for degradation
ERAD
- misfolded protein in ER is translocated to cytoplasm by chaperones entering the ubiquitin process
Lysosomal Degradation
- membrane bound organelles containing proteases that will degrade exogenous proteins
Autophagy
- maintains normal functioning by protein degradation (appears in stress)
Apoptosis
- programmed cell death
Autophagy and Lysosomal Degradation
- uptake and recycling of nutrients and receptors
- merges with autophagic pathway
- can degrade exogenous or endogenous proteins
- double membrane structure forms by vesicle nucleation around cytoplasmic contents and forms a autophagosome
- fusion of the autophagosome with lysosome becomes a autolysosome
- degradation produces amino acids, fatty acids that can be recycled
Defective Autophagy
- When the accumulation of autophagosomes becomes larger than the autophagic degradation, this can lead to neurodegeneration and alzheimer’s
Causes of Increase autophagosomes
- aberrant activation of autophagy
- disruption of autophagosome-lysosome function
- inhibition of lysosome acidification
Ubiquitiin-Proteasomal System
- cell control, cell differentiation, and stress response
- must be covalently modified on a lysine
3 Steps
- E1 (activating): ATP hydrolysis to add ubiquitin to a cysteine
- E2 (conjugating): receives ubiquitin on cysteine (transfers from E1 to E2)
- E3 (ligase): specific recognition of protein to be degraded as it transfers the ubiquitin from E2 to the lysine of the substrate
MUST CONTAIN AT LEAST 4 UBIQUITIN
Proteasome
20S + 19S = 26S Proteasome
20S
core complex consisting of alpha and beta subunits
able to degrade short unfolded non-ubiquinated proteins
trypsin, caspase, and chymotrypsin activity
19 S
contains 2 molecules
regulatory cap consisting of multiple subunits
responsible for deubiquination, protein unfolding, and feeding the proteasome
Oxidative Stress to Proteasome
ECM29 sequests the 19S caps to be bound and held to the HSP70 protein
20S is free to degrade oxidized proteins
Key Difference between Lysosome and UPS
Target Specificity
Degron: recognition sequence or structure for an E3 ligase
Ex.
- N end rule: N terminal sequence of protein is recognized and the 2nd residue can be destabilized (Arg, Leu, Phe)
- PEST Sequences (Proline, Glutamic Acid, Serine, Threonine
- PTM through phosphorylation
Protein Misfolding in Cancer
- unregulated cell division requires increased protein synthesis
- cancer cells are susceptible to drugs that alter proteostasis
MORE SUSPECITBLE TO PROTEOLYSIS THAN NORMAL CELLS
