Explain the molecular mechanics by which a prion protein (PrP^Sc) induces conformational changes in normal cellular prion protein (PrP^C), focusing on the structural transition from alpha-helices to beta-sheets. Discuss the concept of 'strains' in prion biology and how different conformations encode distinct pathological phenotypes. Propose a theoretical small-molecule therapeutic strategy that stabilizes the native alpha-helical structure without disrupting the protein's normal physiological function, addressing the blood-brain barrier challenge.