Figure 2. Different modes of multivalent interactions in synthetic and natural systems undergoing liquid-liquid phase separation.

A) (Left) Nephrin contains three phospho-Tyr (pTyr) motifs (small blue circles), which interact with the SH2 domain (dark blue) on Nck. Nck also, contains three SH3 domains (blue), which bind to the numerous proline-rich motifs (PRM) (pink) in neural Wiskott-Aldrich syndrome protein (N-WASP). (Right) Engineered multivalent model systems, consisting of multiple SH3 or SUMO domains (blue), paired with multivalent ligands which contain multiple proline-rich or SUMO-interaction- motifs, PRM or SIM respectively (pink). See¹⁹ for details.

B) Edc3 dimerizes via its YJefN domain (green rectangles) and binds to the helical leucine-rich motifs (purple triangles) in Dcp2 via its LSm domain (blue). See²⁷ for details.

C) Nucleophosmin (NPM1) assembles into pentamers via its oligomerizing domain (green triangles) and binds to proteins that contain positively charged Arg-rich linear motifs (R-motifs) (blue rectangles) via its negatively charged acidic, tracts (pink rectangles). NPM1 can also bind to potentially multivalent nucleic acids via its nucleotide binding domain (not shown). See²³ for details.

D) RNA binding protein PTB interacts with UCUCU tracts in RNA (connected by AAAA linkers) via its RNA recognition motifs (blue squares). See¹⁹ for details.

E) Association of intrinsically disorder regions (IDRs) via cation-pi interactions between aromatic and basic residues, as in DDX4²².

F) Patterned intermolecular electrostatic interactions between acidic and basic tracts, as in the interactions between the Nephrin intracellular domain (NICD) and positively charged partners, such as supercharged GFP (scGFP)⁴³.

G) Patterned electrostatic interactions between acidic and basic tracts in a single molecular species, as in P granule protein Laf1³³.

H) Polypeptide backbone interactions between β-strands in the polypeptide, as in FUS and hnRNPA1/2^15,34,42,48.

I) Phase diagram as a function of the concentrations of modules present in polymerizing multivalent components that are essential for Condensate formation. Phase separation will be promoted by increasing cellular concentration of component A.

J) Regulation of Condensate formation by increase in critical concentration through increasing the valency of A and/or B or the affinity between A and B. Effective valency may be increased by the presence of a third interacting component as shown in the inset.

K) Regulation of Condensate formation by decrease in the intrinsic solubility of component A. As molecule A becomes less soluble, phase separation can occur at lower concentrations of A.