THE ROLE OF COPPER IN PRION PROTEIN BIOLOGY

Washington University, Saint Louis MO

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Abstract

DESCRIPTION (From the applicant's abstract): Prion diseases are neurodegenerative disorders that result from changes in the conformation of a single, highly unusual membrane glycoprotein called PrP (prion protein). This molecular transition converts a normal version of the protein (PrPc) into a pathogenic form (PrPsc) that constitutes the major component of an unprecedented type of infectious particle (prion) devoid of nucleic acid. Although a wealth of information is now available about the role of PrPsc in the disease process, relatively little is known about the normal, physiological function of PrPc. Aside from its intrinsic biological interest, identifying the function of PrPc is likely to be important in understanding the pathogenesis of prion disease, as it has been suggested that impairment of this function as a result of conversion to PrPsc may explain some features of the disease phenotype. Several lines of evidence have emerged recently suggesting that PrPc may play an important role in the cellular metabolism of the essential trace metal, copper. The most compelling results are that copper binds with low micromolar affinity to PrPc, that membrane fractions from the brains of PrP-null mice show 5 percent of the normal content of ionic copper, and that neuronal Cu-Zn superoxide dismutase from these mice is less enzymatically active and incorporates less radioactive copper than the enzyme from normal mice. In addition, my own laboratory has recently shown that copper ions rapidly and dramatically alter the cellular trafficking of PrPc in cultured neurons. Taken together, these findings constitute the most substantial clues to the normal function of PrPc to emerge in the 15 years since the protein was discovered. They suggest the hypothesis that PrPc may function in cellular pathways responsible for uptake delivery, or excretion of copper ions. The results also raise the possibility that copper metabolism may be altered during prion diseases, and that manipulation of copper levels may be useful in treatment of the disorders. In this application, we will investigate these ideas by (1) analyzing the interactions between PrPc and copper at the cellular and biochemical levels in mammalian cells, (2) by using the yeast S. cerevisiae to elucidate the role of PrPc in copper trafficking, (3) by characterizing the interplay between copper and the disease-specific isoform PrPsc, and (4) by using PET to image the distribution of radioactive copper in living mice.