BPS2026 – Molecular structure modulates condensate formation of polyubiquitin cargo with ubiquitin-binding proteins

Polyubiquitin (polyUb) chains play vital roles in vesicle trafficking, and protein condensates and clustering have recently received attention as potential mechanisms to regulate polyUb processes, though the precise mechanisms by which ubiquitylated cargos self-organize remain unclear. To investigate this process, we examined how molecular features such as conformational freedom and multivalency impact the formation and properties of condensates between polyUb cargo and proteins containing ubiquitin-binding domains (UBDs). Using synthetic and engineered UBD constructs as well as the physiological VPS27-HSE1 complex, we observed condensate formation with differing potency and characteristics, as visualized by fluorescence microscopy and fluorescence recovery after photobleaching (FRAP). Together with quantitative characterization using atomic force microscopy (AFM), these findings contribute to developing a framework linking molecular architecture to condensate properties and their potential physiological significance in organizing ubiquitylated cargo at membranes.