Sequence effects on internal structure of droplets of associative polymers

Intrinsically disordered proteins (IDPs) can form liquid -like membraneless organelles, gels, and fibers in cells and in vitro. In this study, we propose a simple model of IDPs as associative polymers in poor solvent and explore the formation of transient liquid droplets and their transformation into solid -like aggregates. We use Langevin dynamics simulations of short polymers with two stickers placed symmetrically along their contour to study the effect of the primary sequence of these polymers on their organization inside condensed droplets. We observe that the shape, size, and number of sticker clusters inside the droplet change from a long cylindrical fiber to many compact clusters as one varies the location of stickers along the chain contour. Aging caused by the conversion of intramoleclular to intermolecular associations is observed in droplets of telechelic polymers but not for other sequences of associating polymers. The relevance of our results to condensates of IDPs is discussed. SIGNIFICANCE Intrinsically disordered proteins (IDPs) are important ingredients of most biomolecular condensates in cells. The formation of these condensates is governed by liquid -liquid phase separation, in which IDPs condense into liquid droplets. Recent studies show that condensed liquid droplets of many IDPs, such as T-proteins and niacleoP orins' become. 'solid -like aggregates (fibers and gels) after a long incubation time. Here we model IDPs as associative polymers and explore the dependence of internal morphology of condensates on the primary structure of IDPs. Our model captures the phenomenon of aging in droplets of associative polymers.