Biology subjects

Ditlev, J.

Publications and source records attributed to Ditlev, J..

3 recordsLinked to original sources

bioRxiv2025

Biomolecular phase boundaries are described by a solubility product that accounts for variable stoichiometry and soluble oligomers

The solubility product is a rigorous description of the phase boundary for salt precipitation and has previously been shown to qualitatively describe the condensation of biomolecules. Here we present a derivation of the solubility product showing that the solubility product is also a robust description of biomolecule phase boundaries if care is taken to account for soluble oligomers and variable composition within the dense phase. Our calculation describes equilibrium between unbound monomers, the dense phase, and an ensemble of oligomer complexes with significant finite-size contributions to their free energy. The biomolecule phase boundary very nearly resembles the power law predicted by the solubility product when plotted as a function of the monomer concentrations. However, this simple form is concealed by the presence of oligomers in the dilute phase. Accounting for the oligomer ensemble introduces complexities to the power law phase boundary including re-entrant behavior and large shifts for stoichiometrically matched molecules. We show that allowing variable stoichiometry in the dense phase expands the two phase region, which appears as curvature of the phase boundary on a double-logarithmic plot. Furthermore, this curvature can be used to predict variations in the dense phase composition at different points along the phase boundary. Finally, we show how the solubility product power law can be identified in experiments by using dilute phase dissociation constants to account for the oligomer ensemble.

biophysics↗

bioRxiv2022

Coupling of protein condensates to ordered lipid domains determines functional membrane organization

During T-cell activation, the transmembrane adaptor Linker of Activation of T-cells (LAT) forms biomolecular condensates with Grb2 and Sos1, facilitating signaling. LAT has also been associated with cholesterol-rich condensed lipid domains. However, the potential coupling between protein condensation and lipid phase separation and its role in organizing T-cell signaling were unknown. Here, we report that LAT/Grb2/Sos1 condensates reconstituted on model membranes can induce and template lipid domains, indicating strong coupling between lipid- and protein-based phase separation. Correspondingly, activation of T-cells induces protein condensates that associate with and stabilize raft-like membrane domains. Inversely, lipid domains nucleate and stabilize LAT protein condensates in both reconstituted and living systems. This coupling of lipid and protein assembly is functionally important, since uncoupling of lipid domains from cytoplasmic protein condensates abrogates T-cell activation. Thus, thermodynamic coupling between protein condensates and ordered lipid domains regulates the functional organization of living membranes. SUMMARYMembrane-associated protein condensates couple to ordered membrane domains to determine the functional organization of T-cell plasma membranes

cell biology↗

bioRxiv2020

The role of sigma-1 receptor in organization of endoplasmic reticulum signaling microdomains

Sigma 1 receptor (S1R) is a 223 amino acid-long transmembrane endoplasmic reticulum (ER) protein. S1R modulates activity of multiple effector proteins but its signaling functions are poorly understood. We here test the hypothesis that biological activity of S1R in cells can be explained by its ability to interact with cholesterol and to form cholesterol-enriched microdomains in the ER. Using reduced reconstitution systems, we demonstrate direct effects of cholesterol on S1R clustering. We identify a novel cholesterol-binding motif in the transmembrane region of S1R and demonstrate its importance for S1R clustering. We demonstrate that S1R-induced membrane microdomains have increased local membrane thickness. Increased local cholesterol concentration and membrane thickness in these domains can modulate signaling of inositol-requiring enzyme 1 (IRE1) in the ER. Further, S1R agonists cause reduction in S1R clusters, suggesting that biological activity of S1R agonists is linked to remodeling of ER membrane microdomains.

cell biology↗