Polyubiquitin ligand-induced phase transitions are optimized by spacing between ubiquitin units

• DOI: 10.1073/pnas.2306638120
• Publication Date: 2023-10-12T17:35:40Z
• Authors: Sarasi K. K. Gala...; Thuy P. Dao; Suzanne E. Enos; Antara Chaudhuri; Jeremy D. Schmit; Carlos A. Castañeda
• Keywords: Binding Sites; Ubiquitin; Ubiquitination; Biological Sciences; Polyubiquitin; Ligands

Biomolecular condensates form via multivalent interactions among key macromolecules and are regulated through ligand binding and/or posttranslational modifications. One such modification is ubiquitination, the covalent addition of ubiquitin (Ub) or polyubiquitin chains to target macromolecules. Specific between partner proteins, including hHR23B, NEMO, UBQLN2, regulate condensate assembly disassembly. Here, we used a library designed hubs UBQLN2 as model systems for determining driving forces ligand-mediated phase transitions. Perturbations either UBQLN2-binding surface Ub spacing units reduce ability modulate behavior. By developing an analytical based on polyphasic linkage principles that accurately described effects different separation, determined introduction incurs significant inclusion energetic penalty. This penalty antagonizes polyUb scaffold multiple molecules cooperatively amplify separation. The extent which promote separation encoded in spacings units. modulated by linkages architectures, thus illustrating how code regulates functionality emergent properties condensate. naturally occurring linear already optimized with UBQLN2. We expect our findings extend other condensates, emphasizing importance properties, concentration, valency, affinity, sites studies designs condensates.