Understanding epigenetic inheritance and the structures of non-amyloid prion condensates using deep mutagenesis scans

Intrinsically disordered regions (IDRs) are pervasive in eukaryotic proteomes despite their poor evolutionary conservation.

IDRs have recently gained considerable interest as drivers of the formation of biomolecular condensates, representing a novel fundamental principle of eukaryotic subcellular organization.

However, a detailed mechanistic description of how intra and intermolecular interactions drive the formation, stability and physical properties of condensates is lacking.In this project, we will apply deep mutagenesis scans (DMS) to gain insight into sequence-function relationships of IDRs using the remarkable yeast [SMAUG+] non-amyloid prion as a model system. [SMAUG+] is induced through transient overexpression of the RNA binding protein Vts1, leading to the formation of gel-like condensates that are epigenetically inherited through cell divisions.

In addition, [SMAUG+] condensates can act as protein-based infectious agents that transform naïve cells.

We propose to massively mutagenize Vts1 IDRs and measure the individual and combinatorial effects of IDR mutations on [SMAUG+] formation and stability.

This will allow us to gain insight into the mechanisms of condensate formation and prionogenic activity of [SMAUG+], and potentially uncover the structures of condensed [SMAUG+] through analysis of the genetic interactions (epistasis) between mutations.

Finally, we will use automated microscopy of selected mutants to understand how mutations affect the inheritance of the prion.The insights obtained from this DMS analysis will be combined with information from previous genome-wide prion formation assays in order to build predictive models of non-amyloid prionogenic activity from protein sequence.

The ultimate goal is to translate these models into metazoan proteomes, including human, in order to define novel non-amyloid prion candidates and begin to characterize their functions in non-genetic protein-based inheritance in normal development and in disease.