Soren Westrey
New York University
Multivalency Tunes the Composition and Architecture of Biomolecular Condensates
Biomolecular condensates formed by phase separation are recognized as key organizers of cellular biochemistry, yet the impact of small molecules on condensate composition and spatiotemporal dynamics remains unclear. Understanding these subtle changes can reveal dynamic regulatory mechanisms of condensates. Using holographic microscopy, we analyze thousands of condensates in a substrate and label-free manner to minimize perturbations to the system. This technique provides highly precise measurements of condensate size and refractive index, a proxy for dense phase concentration. We investigate the impact of magnesium and other cationic small molecules on the dense phase concentration and size of condensates formed by the protein PopZ. We find that condensation by the addition of cations affords a broad range of 10 to 200-fold increase in protein concentration within the condensate depending on the concentration and valency of the cation. Increasing cation valency of the small molecule resulted in non-monotonic increases in dense phase concentrations and smaller condensate sizes. With super-resolution microscopy and molecular dynamics simulations, we find first that increasing valency in the cation increases dynamic motion of PopZ within the condensate. However, MD simulations demonstrate that higher valency cations interact with more PopZ molecules at a time but with less efficiency, allowing freer motion of protein in the condensate. These insights and methods suggest a mechanism by which cells may regulate intracellular small molecule concentrations and offer insight into potential drug impacts on the internal dynamics and composition of condensate systems.
Biomolecular condensates formed by phase separation are recognized as key organizers of cellular biochemistry, yet the impact of small molecules on condensate composition and spatiotemporal dynamics remains unclear. Understanding these subtle changes can reveal dynamic regulatory mechanisms of condensates. Using holographic microscopy, we analyze thousands of condensates in a substrate and label-free manner to minimize perturbations to the system. This technique provides highly precise measurements of condensate size and refractive index, a proxy for dense phase concentration. We investigate the impact of magnesium and other cationic small molecules on the dense phase concentration and size of condensates formed by the protein PopZ. We find that condensation by the addition of cations affords a broad range of 10 to 200-fold increase in protein concentration within the condensate depending on the concentration and valency of the cation. Increasing cation valency of the small molecule resulted in non-monotonic increases in dense phase concentrations and smaller condensate sizes. With super-resolution microscopy and molecular dynamics simulations, we find first that increasing valency in the cation increases dynamic motion of PopZ within the condensate. However, MD simulations demonstrate that higher valency cations interact with more PopZ molecules at a time but with less efficiency, allowing freer motion of protein in the condensate. These insights and methods suggest a mechanism by which cells may regulate intracellular small molecule concentrations and offer insight into potential drug impacts on the internal dynamics and composition of condensate systems.
