Complexes between cationic pyridylphenylene dendrimers and ovine prion protein: do hydrophobic interactions matter?

Here, the interactions between cationic pyridylphenylene dendrimers of the second, third and fourth generations and full-length ovine prion protein (PrP) were studied using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and tryptophan fluorescence measurements. A molecular dynamic (MD) study was performed to predict the most possible binding sites for the dendrimer interactions with the protein. All the dendrimers used acted as effective quenchers of fluorescence of the tryptophan residues. The quenching constants calculated according to the Stern-Volmer equation allowed us to quantitatively estimate the efficiency of the dendrimer-protein interactions. ITC data revealed the driving force of the complexation: electrostatic interactions assisted by hydrophobic interactions. Due to the latter, the dendrimer and PrP form complexes which are stable towards the addition of a salt and of the oppositely charged polymer. These results allowed us to propose the mechanism and the model of the pyridylphenylene dendrimer interactions with full-length PrP.