Phase behavior of intrinsically disordered prion‐like domains

Abstract

Phase transitions underlie cellular compartmentalization and mediate fundamental biological processes. How they are encoded in the protein sequence is therefore important. Here, we use biophysical experiments, theory, and simulations to generate a conceptual stickers‐and‐spacers framework to understand phase behavior of intrinsically disordered prion‐like low‐complexity domains (PLCDs) of RNA‐binding proteins. Stickers form non‐covalent inter‐ and intramolecular crosslinks, whereas spacers enable or suppress the formation of these crosslinks. We have previously shown that aromatic residues are the stickers in the PLCD of hnRNPA1. Here, we demonstrate that tyrosine is a stronger sticker than phenylalanine and account for interactions of charged residues. Negatively charged residues are solubilizing spacers. Arginines act as stickers through pairwise interactions with aromatic residues, while lysines weaken sticker‐sticker interactions. Low or high values of the net charge per residue weaken phase separation via mean‐field electrostatic effects, while a net charge per residue close to zero minimizes solubility and is optimal for phase separation. We further characterize the function of spacer residues, particularly that of the two most frequent spacer types glycine and serine, to ask whether serine acts as a weak sticker via its side chain. Instead, we find that increasing serine contents decreases the driving force for phase separation in agreement with the higher effective solvation volume of serine vs glycine. Our analytical and coarse‐grained models accurately predict PLCD phase behavior.