Distinct effects of Cu2+-binding on oligomerization of human and rabbit prion proteins.

The cellular prion protein (PrPC) is a kind of cell-surface Cu2+-binding glycoprotein. The oligomerization of PrPC is highly related to transmissible spongiform encephalopathies (TSEs). Cu2+ plays a vital role in the oligomerization of PrPC, and participates in the pathogenic process of TSE diseases. It is expected that Cu2+-binding has different effects on the oligomerization of TSE-sensitive human PrPC (HuPrP(C)) and TSE-resistant rabbit PrPC (RaPrPC). However, the details of the distinct effects remain unclear. In the present study, we measured the interactions of Cu2+ with HuPrP(C) (91-230) and RaPrPC (91-228) by isothermal titration calorimetry, and compared the effects of Cu2+-binding on the oligomerization of both PrPs. The measured dissociation constants (K-d) of Cu2+ were 11.1 +/- 2.1 mu M for HuPrP(C) and 21.1 +/- 3.1 mu M for RaPrPC. Cu2+-binding promoted the oligomerization of HuPrP(C) more significantly than that of RaPrPC. The far-ultraviolet circular dichroism spectroscopy experiments showed that Cu2+-binding induced more significant secondary structure change and increased more beta-sheet content for HuPrP(C) compared with RaPrPC. Moreover, the urea-induced unfolding transition experiments indicated that Cu2+-binding decreased the conformational stability of HuPrP(C) more distinctly than that of RaPrPC. These results suggest that RaPrPC possesses a low susceptibility to Cu2+, potentially weakening the risk of Cu2+-induced TSE diseases. Our work sheds light on the Cu2+-promoted oligomerization of PrPC, and may be helpful for further understanding the TSE-resistance of rabbits.