Abstract

Proteins can transition between a wide range of organisational states, from soluble monomers to disordered phases and ordered structures [1,2]. Experiments have shown that, depending on protein and salt concentration, lysozyme-sodium thiocyanate solutions exhibit homogeneous solution states, coexistence between crystalline and liquid phases, or liquid-liquid phase separation. The corresponding phase boundaries can be shifted by applying an external electric field [3,4]. To gain deeper insight into the mechanisms underlying these phase transformations, we present a coarse-grained model of lysozyme in sodium thiocyanate solution, representing the protein as an ellipsoid decorated with charged and adhesive surface patches. Counterions and monovalent salt are treated explicitly via excluded-volume repulsion and Coulombic interactions. Using the ESPResSo software package [5], we perform molecular dynamics simulations with explicit solvent. We investigate (i) how patch size and salt–patch interactions influence ion distributions around a single protein, with and without an external electric field, and (ii) the resulting effective interactions between two proteins as functions of patch properties, salt concentration, and applied electric field.

References

[1] J. D. Gunton, A. Shiryayev, and D. L. Pagan, Protein Condensation: Kinetic Pathways to Crystallization and Disease, Cambridge University Press (2007). [2] A. Stradner and P. Schurtenberger, Soft Matter, 16, 307–323 (2020). [3] D. Ray, M. Madani, J. K. G. Dhont, F. Platten, and K. Kang, The Journal of Physical Chemistry Letters, 15 (31), 8108–8113 (2024).

[4] D. Ray, M. Madani, J. K. G. Dhont, F. Platten, and K. Kang, Electric field-induced control of protein crystal morphology, 21 (16), 3012–3021 (2025).

[5] R. Weeber et al., Comprehensive Computational Chemistry, 3, 578–601 (2024).