Biology subjects

Chan, H. S.

Publications and source records attributed to Chan, H. S..

3 recordsLinked to original sources

bioRxiv2025

Sequence-based prediction of condensate composition reveals that specificity can emerge from multivalent interactions among disordered regions

While specificity of biomolecular interactions is typically understood to require interactions involving ordered structures, several biomolecular condensates exhibit specificity in the absence of apparent structural order. We have previously shown that condensates composed of the disordered region of MED1 partition specific proteins, mediated by sequence patterns of charged amino acids on the disordered regions of both MED1 and the interacting partner. Whether this specificity is due to an unknown ordered-structure-mediated interaction or from the dynamic multivalent interactions between the patterned charged amino acids in the disordered regions was unresolved. Here we show that a polymer physics-based model that only accounts for multivalent interactions among polymers in a statistical manner can largely explain published data on selective partitioning and make predictions that are subsequently experimentally validated. These results suggest that the specificity of condensate composition is underpinned to a substantial extent by multivalent interactions in the context of conformational disorder.

biophysics↗

bioRxiv2022

Biological condensates form percolated networks with molecular motion properties distinctly different from dilute solutions

Formation of membraneless organelles or biological condensates via phase separation hugely expands cellular organelle repertoire. Biological condensates are dense and viscoelastic soft matters instead of canonical dilute solutions. Unlike discoveries of numerous different biological condensates to date, mechanistic understanding of biological condensates remains scarce. In this study, we developed an adaptive single molecule imaging method that allows simultaneous tracking of individual molecules and their motion trajectories in both condensed and dilute phases of various biological condensates. The method enables quantitative measurements of phase boundary, motion behavior and speed of molecules in both condensed and dilute phases as well as the scale and speed of molecular exchanges between the two phases. Surprisingly, molecules in the condensed phase do not undergo uniform Brownian motion, but instead constantly switch between a confined state and a random motion state. The confinement is consistent with formation of large molecular networks (i.e., percolation) specifically in the condensed phase. Thus, molecules in biological condensates behave distinctly different from those in dilute solutions. This finding is of fundamental importance for understanding molecular mechanisms and cellular functions of biological condensates in general.

cell biology↗

bioRxiv2019

Piezo1 Induces Local Curvature in a Mammalian Membrane and Forms Specific Protein-Lipid Interactions

Touch, hearing, and blood pressure control require mechanically-gated ion channels that convert mechanical stimuli into electrical currents. Piezo1 and Piezo2 were recently identified as essential eukaryotic mechanically-gated ion channels, yet how they respond to physical forces remains poorly understood. Here we use a multi-disciplinary approach to interrogate the interaction of Piezo1 with its lipid environment. We show that individual Piezo1 channels induce significant local curvature in the membrane that is magnified in a cooperative manner to generate larger curved Piezo1 pits. Curvature decreases under lateral membrane tension, consistent with a hypothesis that force detection can involve sensing changes to local curvature. The protein alters its local membrane composition, enriching specific lipids and forming essential binding sites for phosphoinositides and cholesterol that are functionally relevant and often related to Piezo1-mediated pathologies. Finally, we show that Piezo1 alters the expression of lipid-regulating proteins and modifies the cellular lipidome. In short, we find that lipids influence Piezo1 activity and Piezo1 influences the local morphology and composition of the bilayer as well as the cellular lipidome.

biophysics↗