Hydrophobic residues advance the onset of simple coacervation in intrinsically disordered proteins at low densities: Insights from field theoretical simulations studies

Intrinsically disordered proteins (IDPs) have engendered a definitive change in the way we think about the classical "sequence-structure-function" dogma. Their conformational pliability and rich molecular recognition features endow them with the ability to bind to diverse partners and predispose them to an elaborate functional armory. And of late, with studies on IDP-based liquid-liquid phase separation (LLPS) leading to formation of functional subcellular coacervates - best described as "membrane-less organelles (MLOs)", IDPs are also bringing about paradigmatic changes in the way we think about biomolecular assemblies and subcellular organization. Though it is well recognized that the phase behavior of a given IDP is tightly coupled to its amino-acid sequences, there are only a few theories to model polyampholyte coacervation for IDPs. Recently, Joan-Emma Shea and co-workers used field theoretical simulations (FTS) to elucidate the complete phase diagram for LLPS of IDPs by considering different permutations of 50-residues chain representing 25 Lysine and 25 Glutamic acid [1]. Our work is an extension of that FTS framework where we develop and solve an augmented Hamiltonian that also accounts for hydrophobic interactions in the chain. We show that incorporation of hydrophobic interactions result in an advanced onset of coacervation at low densities. The patterning of hydrophobic, positive and negative residues plays important role in determining relative differences in the onset of phase separation. Though still very coarse-grained, once additional chemical specificities are incorporated, these high throughput analytical theory methods can be used as a starting point for designing sequences that drive LLPS.