correcting protein defects

Question 1

protein only hypothesis

Answer 1

• two convalently identical forms of PrP. PrPc is non-pathogenic. PrPsc is pathogenic. only differ by conformation
• they exist in an equilibria
• when several PrPsc interact, bind via b sheet interactions
• complex is stable and serves as a “seed” for more
• think it is a self propagating infectious agent (not viral) because reduced infectivity with protein denaturant and seeding with PrPsc causes many more PrPc to change into aggregated conformation

Question 2

how to treat PrPsc aggregates

Answer 2

1. silence siRNA to make less PrP
2. stabilize PrPc by binding to it
3. immunize with PrP-PrP dimer
4. disassemble aggregates with Hsp100 class

Question 3

toxic protein conformations

Answer 3

1. pore hypothesis - evidenced from islet amyloid polypeptide (secreted with insulin)
   - still developing oligomers are more toxic than mature amyloid fibers
   - as they are developing they diffuse through membrane and form a pore
   - when big enough, B fibers bud off into cytosol
   - if you introduce mature fibers into cell, they may just diffuse into cytosol rather than disrupting membrane
2. receptor hypothesis: AB42 studies
   - prion oligomers bind receptors and alter signaling
   - glutamate receptors in AD and CJD
   - try to prevent Ab42 and PrPc from binding glutamate to treat

Question 4

how a defect changes protein properties

Answer 4

1. Prion disease - equilibrium favors PrPsc.allows nucleation of B structure
2. Apolioprotein E: ApoE4 isoform forms a salt bridge between Arg and glutamate. causes preferential binding of VLDL and ABeta (risk for CVD and AD)
3. transthyretin amyloidosis: TTR binds thyroxine. mutated form favors monomeric form that makes amyloid fibers. multiple organ failure if this happens all over the body.

Question 5

how toxic folds kill and cause disease

Answer 5

amyloid cascade hypothesis: mature fibrils cause death and disease
other hypotheses: amyloids are side effect. developing oligomers cause disease.

Question 6

how small molecules can disrupt aggregation

Answer 6

AD - disrupting salt bridge in ApoE4 would lower risk

TTR amyloidosis: bind to stabilize tetramer form