Biology subjects

Case, L. B.

Publications and source records attributed to Case, L. B..

5 recordsLinked to original sources

bioRxiv2026

An intrinsically disordered adaptor protein controls the size and composition of EGFR condensates on membranes

Receptor phase separation is common in signaling pathways, yet mechanisms that limit condensate size and drive their dissolution remain poorly understood. For example, phosphorylated EGFR forms large micron-scale condensates in vitro, but assembles into smaller nanoscale clusters in cells, suggesting cellular regulation of condensate size. Here, we show that the intrinsically disordered adaptor protein GAB1 actively dissolves EGFR condensates and re-nucleates smaller, compositionally distinct assemblies in reconstituted supported lipid bilayers and simulations. Dissolution requires unphosphorylated tyrosines within the GAB1 intrinsically disordered region, and tyrosine phosphorylation acts as a regulatory switch that abolishes this activity. GAB1-nucleated assemblies require PH domain-driven oligomerization, which is inhibited by phosphoinositide lipids, linking membrane composition to nucleation. These results uncover two unexpected regulatory features in signaling pathways. First, unphosphorylated tyrosines may function broadly to regulate condensate size or stability, since similar tyrosine-based sequence features are found across hundreds of proteins, including many that function in signal transduction. Additionally, PH domains may play a broader role in protein oligomerization and receptor organization, as an AlphaFold screen reveals dozens of additional PH domains predicted to self-associate. Together, these results establish general mechanisms that function as modular tools for reprogramming signaling through receptor reorganization and may enable new approaches to target such pathways in disease.

biophysics↗

bioRxiv2026

AI-discovered protein fragments as generalizable regulators of biomolecular condensates

Biomolecular condensates are a major driver of cellular organization; however, we lack a predictable and systematic approach to modulate their underlying multivalent interactions. Here, we demonstrate a generalizable AI-driven method for designing protein fragments to control condensate formation, applying this approach across G3BP1, SARS-CoV-2 nucleocapsid, TDP-43, and focal adhesion kinase (FAK). Computationally screening 2,235 fragments, we selected 18 for experimental investigation, attaining a 50% success rate. Furthermore, predicted fragment binding modes align with their activities, revealing known and novel interactions driving condensate formation. For example, a fragment which suppresses FAK condensates in mammalian cells uncovered an interdomain interaction required for phase separation. Together, our results establish AI-guided protein fragment discovery as a generalizable strategy to dissect and control the molecular interactions that govern biomolecular condensates.

biophysics↗

bioRxiv2025

Kinase condensates enrich ATP and trigger autophosphorylation

Kinase-mediated signal transduction regulates most cellular processes, and autophosphorylation is a common mechanism to activate kinases. Many kinases undergo phase separation to form condensates. Despite the central role of autophosphorylation in regulating kinase activity, how condensates impact kinase autophosphorylation has not been systematically studied. Using biochemical reconstitution and cellular studies, we find that phase separation can concentrate kinases to effectively trigger the trans-autophosphorylation of the tyrosine kinases FAK and Abl, as well as the serine/threonine kinase Mst2. Moreover, kinase condensates can create a chemical environment that enriches ATP, and positively charged intrinsically disordered regions are one feature that enrich ATP into condensates. Thus, kinase phase separation is a general mechanism to activate kinase signaling pathways by locally concentrating both kinases and ATP to trigger autophosphorylation.

biophysics↗

bioRxiv2023

Membrane-induced 2D phase separation of focal adhesion proteins

Focal adhesions form liquid-like assemblies around activated integrin receptors at the plasma membrane. Made up of hundreds of proteins, focal adhesions are dynamic structures which can assemble and disassemble quickly, withstand strong actomyosin-applied forces, and form highly stable complexes. How they achieve these flexible characteristics is not well understood. Here, we use recombinant focal adhesion proteins to reconstitute the core structural machinery in vitro, with the goal of understanding the underlying protein dynamics and interactions. We observe liquid-liquid phase separation of the core focal adhesion proteins talin and vinculin for a spectrum of conditions and in combination with several interaction partners. Intriguingly, we show that membrane binding triggers phase separation of these proteins on the membrane, which in turn induces the enrichment of integrin in the clusters. We also introduce a novel experimental setup to probe talin-membrane interactions down to the single protein level. Our results suggest that membrane composition triggers condensate assembly at the membrane, a regulatory mechanism which could widely apply to membrane-localized biomolecular condensates and provide a pathway of how spatial organization of lipids within the membrane can couple into the cytosol.

cell biology↗

bioRxiv2021

Synergistic Phase Separation of Two Pathways Promotes Integrin Clustering and Integrin Adhesion Complex Formation

Integrin adhesion complexes (IACs) are integrin-based plasma membrane-associated compartments where cells sense environmental cues. The physical mechanisms and molecular interactions that mediate nascent IAC formation are unclear. We found that both p130Cas ("Cas") and Focal adhesion kinase ("FAK") undergo liquid-liquid phase separation in vitro under physiologic conditions. Cas- and FAK- driven phase separation is sufficient to reconstitute kindlin-dependent integrin clustering in vitro. In vitro condensates and cellular IACs exhibit similar sensitivities to environmental perturbations including changes in temperature and pH. Furthermore, mutations that inhibit or enhance phase separation in vitro reduce or increase the number of IACs in cells, respectively. Finally, we find that the Cas and FAK pathways act synergistically to promote phase separation, integrin clustering and IAC formation in vitro and in cells. We propose that Cas- and FAK- driven phase separation provides an intracellular trigger for integrin clustering and nascent IAC formation.

cell biology↗