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Prion protein/protein interactions: fusion with yeast Sup35p-NM modulates cytosolic PrP aggregation in mammalian cells

Carmen Krammer^*, Michael H. Suhre, Elisabeth Kremmer, Claudia Diemer^*, Simone Hess, Hermann M. Schätzl^*, Thomas Scheibel and Ina Vorberg^*,1

^* Institute of Virology, Technical University of Munich, Munich, Germany;

Department Chemie, Lehrstuhl für Biotechnologie, Technical University of Munich, Garching, Germany; and

Institute of Molecular Immunology, GSF National Research Center for Environment and Health, Munich, Germany

¹Correspondence: Institute of Virology, Technical University of Munich, Trogerstr. 30, 81675 Munich, Germany. E-mail: vorberg{at}lrz.tum.de

In mammalian prion diseases, an abnormally folded, aggregated form of the prion protein (PrP^Sc) appears to catalyze a conformational switch of its cellular isoform (PrP^C) to an aggregated state. A similar prion-like phenomenon has been reported for the Saccharomyces cerevisiae translation termination factor Sup35p that can adopt a self-propagating conformation. We have compared aggregation propensities of chimeric proteins derived from the Sup35p prion domain NM and PrP in vitro and in the cytosol of mammalian cells. Sup35p-NM and PrP displayed strikingly different aggregation behaviors when expressed in mammalian cells, with NM remaining soluble and cytosolic PrP spontaneously aggregating due to the globular domain of PrP. When fused to PrP_90–230, Sup35p-M exhibited an inhibitory effect for nucleation but increased aggregate growth, potentially by facilitating recruitment of newly synthesized chimeric proteins into the growing aggregates. This effect, however, could, to some extent, be counteracted by the prion-forming region Sup35p-N, thereby increasing aggregate frequency. Interestingly, a lowered nucleation rate was also observed in the presence of the amino-terminal region of PrP, suggesting that Sup35p-M and PrP_23–90 share some biological function in prion protein assembly. Our results provide new insights into prion protein aggregation behaviors, demonstrating the impact of dynamic interactions between prion domains and suggesting that aggregation of yeast and mammalian prion proteins is strongly influenced by yet unidentified cellular conditions or factors.—Krammer C., Suhre, M. H., Kremmer, E., Diemer, C., Hess, S., Schätzl, H. M., Scheibel, T., Vorberg, I. Prion protein/protein interactions: fusion with yeast Sup35p-NM modulates cytosolic PrP aggregation in mammalian cells.

Key Words: Key Words: amyloid • protein misfolding • seeding • nucleation