Intrinsically disordered proteins (IDPs) at physiological conditions have no well-defined, stable structure in extended parts of their polypeptide chains. They participate in many processes in biological cells, including signaling, cell-cycle regulation, and initiation of translation.
IDPs are major components of biomolecular condensates (BCs) that form through liquid-liquid phase separation in biological cells. Despite considerable research on BCs in the cytosol and nucleus, their behavior at cellular membranes remains largely unexplored.
Galectin-3 is a protein comprising an intrinsically disordered N-terminal domain (NTD) and a well-folded carbohydrate recognition domain (CRD) which can bind to glycosphingolipids on the cell membrane. Galectin-3 is known to mediate clathrin-independent endocytosis [1] and has been recently shown to undergo liquid-liquid phase separation [2], but the function of the BCs of galectin-3 in the endocytic pit formation is unknown.
Using dissipative particle dynamics (DPD) simulations, we explore how polymer models resembling galectin-3 sense and respond to membrane curvature. Our findings suggest a generic mechanism by which BCs sense membrane curvature, potentially influencing such cellular processes as endocytosis [3]. To elucidate the conformational dynamics of galectin-3, we have conducted molecular dynamics simulations using the Martini 3 force field. Following the method introduced by Thomasen et al. [4] for rescaling protein-water interactions, we generate a conformational ensemble in good quantitative agreement with data from small angle X-ray scattering experiments [5]. Our simulations reveal large-scale fluctuations between compact and extended conformations of galectin-3, with aromatic residues within the NTD forming most frequent contacts [6].
[1] Lakshminarayan, R., Wunder, C., Becken, U., Howes, M. T., Benzing, C., Arumugam, & Johannes, L. (2014). Galectin-3 drives glycosphingolipid-dependent biogenesis of clathrin-independent carriers. Nature Cell Biology, 16(6), 592-603.
[2] Chiu, Y. P., Sun, Y. C., Qiu, D. C., Lin, Y. H., Chen, Y. Q., Kuo, J. C., & Huang, J. R. (2020). Liquid-liquid phase separation and extracellular multivalent interactions in the tale of galectin-3. Nature Communications, 11(1), 1229.
[3] Anila, M. M., Ghosh, R., & Różycki, B. (2023). Membrane curvature sensing by model biomolecular condensates. Soft Matter, 19(20), 3723-3732.
[4] Thomasen, F. E., Pesce, F., Roesgaard, M. A., Tesei, G., & Lindorff-Larsen, K. (2022). Improving Martini 3 for disordered and multidomain proteins. Journal of Chemical Theory and Computation, 18(4), 2033-2041.
[5] Lin, Y. H., Qiu, D. C., Chang, W. H., Yeh, Y. Q., Jeng, U. S., Liu, F. T., & Huang, J. R. (2017). The intrinsically disordered N-terminal domain of galectin-3 dynamically mediates multisite self-association of the protein through fuzzy interactions. Journal of Biological Chemistry, 292(43), 17845-17856.
[6] Anila, M. M., Rogowski P., & Różycki, B. (2024). Scrutinising the conformational ensemble of the intrinsically mixed-folded protein galectin-3. Under review.