Abstract:
Prion diseases are fatal neurodegenerative disorders of the central nervous system characterized by the
accumulation of a protease resistant form (PrPSc) of the cellular prion protein (PrPC) in the brain. Two
types of cellular prion (PrPC) compounds have been identified that appear to affect prion conversion
are known as Effective Binders (EBs) and Accelerators (ACCs). Effective binders shift the balance in favour
of PrPC, whereas Accelerators favour the formation of PrPSc. Molecular docking indicates EBs and ACCs
both bind to pocket-D of the SHaPrPC molecule. However, EBs and ACCs may have opposing effects on
the stability of the salt bridge between Arg156 and Glu196/Glu200. Computational docking data indicate
that the hydrophobic benzamide group of the EB, GFP23 and the 1-(3,3-dimethylcyclohexylidene)piperidinium
group of the ACC, GFP22 play an important role in inhibition and conversion from SHaPrPC to
SHaPrPSc, respectively. Experimentally, NMR confirmed the amide chemical shift perturbations observed
upon the binding of GFP23 to pocket-D of SHaPrPC. Consistent with its role as an ACC, titration of GFP22
resulted in widespread chemical shift changes and signal intensity loss due to protein unfolding. Virtual
screening of a ligand database using the molecular scaffold developed from the set of EBs identified six of
our compounds (previously studied using fluorescence quenching) as being among the top 100 best binders.
Among them, compounds 5 and 6 were found to be particularly potent in decreasing the accumulation
SHaPrPSc in ScN2a cells with an IC50 of 35 mM and 20 mM.
