Protein Aggregation Flashcards
What are NDD characterised by?
Clinical Symptoms (crossover between AD and PD with dementia) Pathological features (crossover with Tau pathology in AD and PD) Loss of specific neuronal populations
What do all NDD have in common?
Specific protein aggregation and NDD - often linked to a genetic factor, even if rare.
These genetic mutations that directly link to protein aggregation suggestive of a role in the pathogenesis of the disease.
What is the aggregate in AD?
APP and Tau - Genetic mutations in APP - rare
What is the aggregate in PD?
LB and LN characterised by ub-asyn - mutations in SNCA - either polymorphisms (risk), amplifications (dosage effect) or missense (effecting folding) - rare
What is the aggregate in CJD?
Prions - genetic mutations in Prp - rare
What is the aggregate in HD?
Huntingtin - CAG repeats above 34 in Htt gene (95%)
What are the characteristics of aggregated proteins?
Increased beta sheet structure, typically a hydrophobic core, which upon aggregation is typically exposed on the surface of the protein, this can encourage interactions with other proteins.
Prion - 3% in soluble form and 43% in aggregate
What is the definition of an amyloid fibril?
A waxy tissue deposit that takes the form of starch, amylose and amylopetin
Describe the process of protein folding
The folding funnel directs the folding of an unfolded amino acid sequence into a lower free energy conformation, this can take place through multiple pathways; nucleation, hydrophobic collapse. Cells have means of aiding protein folding, or ensuring the “correct” folding by preventing interactions with other proteins during the folding process.
This is through the use of chaperones - chaperones act either co-translationally or post-translationally and are never a part of the final structure. Chaperones are particularly useful in the context of the dynamic microenvironment which is the incredibly crowed
Describe quality control systems in place for folding
The use of heat shock proteins, whose expression is upregulated in time of increased heat, a time at which proteins are more likely to misfold or unfold.
Describe the role of Hsp70
Co-translational role: HSP 70 family bind to proteins as they are synthesized to prevent inappropriate association with other proteins and allow optimal protein configuration. Hsp90 acts downstream of this chaperone.
Describe the role of BiP
Protein found in ER, binds to hydrophobic regions in the internal parts of folding proteins, preventing inappropriate folds and aggregation
Describe the role of Hsp60
Creates a caged structure, the inside of which is hydrophilic, with the outer rims being hydrophobic - enticing the protein inwards, allowing it to perform hydrophobic collapse once inside
What is the UPS?
Ubiquitin Proteasome System - it is a protein quality control system which targets proteins that are dsyfunctional, misfolded or are in a two high a concentration for degradation - it is a major component of cellular proteostasis.
How does the UPS work?
The UPS works through ubiquitination of proteins, which are then targeted for degradation via the 26S proteosome.
- E3 ubiquitin ligase recognises a protein and ligates a ubiquitin to it
- This is done through a process of ubiquitin transfer from an E2 ubiquitin conjugating enzyme
- The subsequent ubiquitins are attached to lysin 48 to generate a polyUb tail
- The polyUb tail is recognised by the 26S proteosome and degraded
Describe the three pathways leading to lysosomes
- CMA
- Macroautophagy (mitophagy is a subset)
- Microautophagy
Why is the CNS so dependent on protein degradation pathways and lysosomes in particular?
Unlike other cells, neurones are post-mitotic so the build up of misfolded proteins can not be diluted through a process of cell division.
Additionally the long, yet thin neuronal processes are paritcularly dependent on efficient trafficking of vesicles required for synpatic transmission. The build up of proteins in these processes could alter synaptic transmission.
What are the 5 steps of CMA?
- Recognition - Hsc70 recognises proteins targetted for proteolysis, this sequence is found in asyn (KFERQ)
- Binding - Binding of Hsc70 and Protein to LAMP2A monomers, this triggers the assembly of a LAMP2A multimer
- Unfolding - The protein is unfolded
- Translocation - Hsc70 is thought to pull through
- Disassociation
Why are newly folded proteins at a great risk for misfolding?
Due to the highly hostile environment of the cytosol - the dense concentration of the cytosol, many proteins which could potential interact with it and disrupt contact formation - some particular contacts are required - for example nucleation and
What are the models of protein folding?
Nucleation condensation model
Hydrophobic collapse
and formation of distal secodnary structures
–> these all fold along a folding funnel
Do only specific proteins form amyloid fibrils?
The SH3 domain of bovine phosphatidyl 3’-kinase forms amyloid fibrils in a low pH - this can demonstrate how environment can act as a huge influence onf the folding
Tell me something promiscouis
Well misfolded proteins have a large percentage of exposed hydrophobic side chains, thus they often have the propensity to be promiscious in terms of there interaction, this is to avoid being encapsulated by a sleeve of water, which presents unfavourable interactions to the protein
Define a chaperone
A chaperone is a protein that can interact and aid the folding of a polypeptide chain into its native state without being present in it final conformation.
Where do E3 ligases transfer their Ubs to and from.
Transferred from E2 Ub conjugating enzyme, to the C terminal glycine on ubiquitin to specific lysine residues on the protein being targetted for degradation
