Quinary structure kinetically controls protein function and dysfunction

TL;DR: The results suggest that quinary structure broadly distinguishes the kinetics of subcellular organization, signal propagation, cytoplasmic inheritance, and proteotoxic activities of low complexity “prion-like” sequences.

Abstract: Protein self-assemblies compartmentalize cellular biochemistry and encode molecular memories; but, they also precipitate incurable degenerative diseases. These activities involve vastly different structures and time scales. Recognizing the dominant role of nucleation in self-assembly kinetics, we hypothesized that quinary structures function, in part, by dictating the energy barrier of nucleation. To investigate, we developed Distributed Amphifluoric FRET (DAmFRET), an approach to characterize protein nucleation in living cells. DAmFRET exploits a photoconvertible fluorophore and heterogeneous levels of expression to quantify a proteins self-assembly as a function of its concentration in living cells. Using DAmFRET, we characterize dozens of self-assembling proteins, and find that structural complexity produces nucleation barriers that kinetically control the proteins cellular activities. Pathological prion-like proteins tended to form metastable condensates, whereas prions with physiological functions did not. Our results suggest that quinary structure broadly distinguishes the kinetics of subcellular organization, signal propagation, cytoplasmic inheritance, and proteotoxicity.