Many Light Touches Convey the Message.

Our attraction to precision and symmetry in everyday life must be put aside to appreciate how natural selection favors networks governed by weak interactions, multivalency, and proteins described as low complexity (LC) and/or intrinsically disordered (ID). Phosphorylation, ubiquitination, and glycosylation of proteins often act as weak docking sites for multivalent adaptor proteins in the formation of membrane-associated and soluble complexes that mediate information flow in cells. Multiple post-translational modification (PTM) sites together with LC and ID regions in proteins can mediate phase transition from soluble complexes to liquid droplets in the cytoplasm or tethering to the membrane. Although compositionally complex and highly dynamic, these systems display remarkable control of specificity, timing, and switch-like behavior in signaling pathways.