Trafficking, turnover and membrane topology of PrP

Cell biological studies of PrP have contributed enormously to our understanding of prion diseases. Like other membrane proteins, PrPC is post-translationally processed in the endoplasmic reticulum and Golgi on its way to the cell surface after synthesis. Cell surface PrPC constitutively cycles between the plasma membrane and early endosomes via a clathrin-dependent mechanism, a pathway consistent with a suggested role for PrPC in cellular trafficking of copper ions. PrP molecules carrying mutations linked to inherited prion diseases display several abnormalities in their biochemical properties, maturation, and localisation that may explain their patho-genicity. Recent results have clarified the role of the proteasome in degradation of PrP, and the properties of a transmembrane form of PrP which may play a neuro-toxic role in prion diseases. Prion diseases are rare neurodegenerative disorders that result from the conformational conversion of a normal cell-surface protein (PrPC) into a protease-resistant, β-sheet-rich form (PrPSc) that is infectious in the absence of nucleic acid. Understanding prion diseases at a mechanisti