Lipid-Mediated DNA-Protein Coupling Reinforces the Mechanics of HP1α-DNA Condensates

Biomolecular condensates formed via liquid-liquid phase separation often contain multiple molecular components whose collective interactions determine their physical properties. However, how different molecular species cooperatively regulate condensate mechanics remains poorly understood. In this study, we integrated Raman-Brillouin imaging with fluorescence recovery after photobleaching (FRAP) analysis to quantify the molecular composition, mobility, and high-frequency viscoelastic responses of multicomponent condensates composed of heterochromatin protein 1α (HP1α), DNA, and lipids. DNA incorporation rendered condensates morphologically distorted yet mechanically soft, while DNA within the condensates exhibited limited mobility, suggesting the formation of partially immobilized DNA-rich structures that shape the condensate morphology without rigidifying the interior. Subsequent lipid incorporation selectively confined HP1α mobility and increased condensate viscoelasticity without altering the DNA dynamics. These results reveal the opposing mechanical effects of DNA and lipids, arising from distinct DNA-protein coupling states within the condensates. DNA-rich structures exhibit dynamics decoupled from HP1α within the same condensates, whereas lipid incorporation enhances effective DNA-protein coupling, thereby reinforcing condensate mechanics. These findings establish lipid-mediated DNA-protein coupling as a key physicochemical mechanism regulating the mechanical properties of multicomponent biomolecular condensates.