N-homocysteinylation of ovine prion protein induces amyloid-like transformation.

Modification of protein lysyl residues by homocysteine (Hcy)-thiolactone generates proteins with altered structures and functions. It has been supposed to be one of the factors inducing protein condensation pathologies. To test a hypothesis that N-homocysteinylation may induce structural changes and in particular amyloidogenic conversion, ovine prion protein (PrP) was modified with Hcy-thiolactone and its physico-chemical properties were studied. N-Hcy-PrP formed insoluble multimers. Mass spectrometry analyses showed that at least K197 and K207 residues of PrP were the sites of N-homocysteinylation. Dynamic light scattering measurements revealed large aggregated N-Hcy-PrP particles of 1μm diameter. They were resistant to proteinase K digestion, and enhanced thioflavin T (ThT)-binding fluorescence, what is characteristic of amyloid structures. Infrared spectroscopy measurements showed increased content of beta-sheet in N-Hcy-PrP compared to unmodified PrP. Epifluorescence microscopy in the presence of ThT revealed cluster-like aggregates of N-Hcy-PrP. The collected data indicate that the N-homocysteinylation causes amyloidogenic transformation of PrP in vitro.