Amino Acids & Proteins MCAT Practice Question
A 34-year-old man with a history of recurrent infections presents with progressive neurological decline, muscle weakness, and cognitive impairment over the past 6 months. Brain MRI reveals cerebellar atrophy. Genetic testing identifies a mutation in the PRNP gene resulting in a prion protein with abnormal folding. A research team studying this patient's prion protein in vitro observes that the mutant prion protein (PrP^Sc) aggregates rapidly when incubated alone, but aggregation is significantly delayed when heat shock proteins (HSPs) are added to the reaction mixture. Which of the following best explains the mechanism by which heat shock proteins delay prion protein aggregation in this experiment?
Answer choices
- AHeat shock proteins covalently modify hydrophobic residues through ubiquitination, directing the misfolded protein to the proteasome for degradation
- BHeat shock proteins act as catalysts to directly convert PrP^Sc back to the normal prion protein conformation through cofactor-mediated reactions
- CHeat shock proteins bind to exposed hydrophobic patches on the misfolded prion protein, preventing intermolecular interactions that would lead to aggregate formationCorrect answer
- DHeat shock proteins phosphorylate serine and threonine residues on the prion protein, stabilizing the native alpha-helical structure
- EHeat shock proteins cleave the N-terminal signal peptide of the prion protein, exposing buried hydrophilic residues that prevent aggregation
- FHeat shock proteins hydrolyze ATP to provide energy that directly unfolds and refolds the prion protein into its native conformation
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