Physics Colloquium: Composition Controls Co-Condensation Morphology and From local asters to global contraction

Physics Colloquium
How a Binding Protein Makes DNA Condense: Composition Controls Co-Condensation Morphology/From local asters to global contraction: How filament length and concentration shape microtubule–motor organization

Dr. Soumik Mitra & Dr. Aravind Rao Karanma
Postdoctoral Researchers,
Rochester Institute of Technology

Abstract:
Cells must compact and organize DNA while keeping it accessible and protected. In bacteria, the DNA-binding protein Dps helps package DNA into dense condensates, offering a simple system for asking a broader question: what controls the shapes and dynamics of biomolecular condensates? Using a continuum model of Dps–DNA co-condensation, I show that the relative amounts of protein and DNA can strongly alter the structures that form. The same attractive interactions can produce compact, droplet-like condensates or extended, interconnected networks, depending on composition. These predictions are consistent with complementary Brownian dynamics simulations from our group, despite the two approaches probing the problem at very different scales. Together, the results suggest that composition can act as a powerful physical control parameter for organizing DNA–protein condensates, with implications for how multicomponent biomolecular materials form and reorganize.
How do simple changes in biological building blocks affect the large-scale structures they form? We pursue this question in a system of microtubules and kinesin motors. Microtubules are stiff protein filaments that help organize the interior of cells, while kinesin motors move along them and generate forces. When combined in vitro, microtubules and motors organize in very different ways—from localized asters to contractile structures spanning the entire system. Using simulations guided by experiments, we examine how two basic properties—the concentration of microtubules and their length—control which of these structures emerges. We find that lower concentrations favor localized asters, while higher concentrations promote asters or system-spanning contraction, with filament length strongly shifting the balance between the two. By connecting simulations with experiments, this work shows how simple microscopic properties can determine whether motor-driven filaments organize locally or collectively across much larger scales.

Speaker Bio: Dr. Soumik Mitra is a postdoctoral researcher in the Das Lab at Rochester Institute of Technology, where he studies the physics of biomolecular condensates and biopolymer networks. He received his PhD from IISER Kolkata, India, working on the statistical physics of charged polymers. Dr. Aravind Rao Karanam is a postdoctoral researcher at the Das Lab at RIT. He studies the dynamics of biopolymer networks using simulations and theory. He received his Ph.D. from UC San Diego where he studied reaction networks in eukaryotic chemotaxis.

Intended Audience:
Beginners, undergraduates, graduates. Those with interest in the topic.

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