Cellular Prion Protein Conformational Shift after Liquid-Liquid Phase Separation Regulated by a Polymeric Antagonist and Mutations

Liquid-liquid phase separation (LLPS) of intrinsically disordered proteins has been associated with neurodegenerative diseases, although direct mechanisms are poorly defined. Here, we report on a maturation process for the cellular prion protein (PrP (c)) that involves a conformational change after LLPS and is regulated by mutations and poly(4-styrenesulfonic acid-co-maleic acid) (PSCMA), a molecule that has been reported to rescue Alzheimer's disease-related cognitive deficits by antagonizing the interaction between PrP (c) and amyloid-beta oligomers (A beta o). We show that PSCMA can induce reentrant LLPS of PrP (c) and lower the saturation concentration (C-sat) of PrP (c) by 100-fold. Regardless of the induction method, PrP (c) molecules subsequently undergo a maturation process to restrict molecular motion in a more solid-like state. The PSCMA-induced LLPS of PrP (c) stabilizes the intermediate LLPS conformational state detected by NMR, though the final matured beta-sheet-rich state of PrP (c) is indistinguishable between induction conditions. The disease-associated E200 K mutation of PrP (c) also accelerates maturation. This post-LLPS shift in protein conformation and dynamics is a possible mechanism of LLPS-induced neurodegeneration.