Specific recognition and recruitment of client molecules by a liquid phase

There are large number of cellular bodies inside the cell which are formed by the condensation of large number of molecules. A small number of these molecules, called “Scaffolds”, produce the phase separated network with liquid-like properties and these networks recruit other molecules, called “Clients”, with the total composition providing functionality. We study a synthetic system of two types of scaffolds (poly-SUMO/poly-SIM) and two types of clients (SUMO/SIM). Based on theoretical modeling, we propose that molecules are highly aligned to form zipper structures and these zippers have defects in the bonding structure that allow for the subsequent formation of a network. We employ a transfer matrix formalism to compute the grand partition function of the zipper structures and to explain the curious non-monotonic client binding behavior observed in experiments. The filament microstructure of the droplet is sensitive to the valence and binding affinity of clients, which provides independent mechanisms to tune the magnitude (via the affinity) and the location (via the valence) of client recruitment. With tuned client affinities, it is possible for the network to specifically select between closely related clients in different regimes of parameter space.