Does tetracycline bind helix 2 of prion? An integrated spectroscopical and computational study of the interaction between the antibiotic and alpha helix 2 human prion protein fragments

We demonstrate here that tetracycline (TC) can strongly interact (K-D = 189 +/- 7 nM) with model peptides derived from the C-terminal globular domain of the prion protein, hPrP [173-195], and that interaction concerns residues within the C-terminal half of the helix 2, a short region previously indicated as endowed with ambivalent conformational behavior and implicated in PrP conversion to the P-sheet-rich, infective scrapie variant. Data have been confirmed by binding studies with the N-terminal truncated 180-195 variant that displays a dissociation constant of 483 +/- 30 nM. Remarkably, TC does not influence the structure of the N-terminally fluoresceinated peptides that both show alpha-helical conformations. Docking calculations and molecular dynamics simulations suggest a direct, strong interaction of the antibiotic with exposed side chain functional groups of threonines 190-193 on the solvent-exposed surface of helix 2.