Martinizing the Variational Implicit Solvent Method (VISM): Solvation Free Energy for Coarse-Grained Proteins

Solvation is a fundamental driving force in many biological processes including biomolecular recognition and self-assembly, not to mention protein folding, dynamics, and function. The variational implicit solvent method (VISM) is a theoretical tool currently developed and optimized to estimate solvation free energies for systems of very complex topology, such as biomolecules. VISM's theoretical framework makes it unique because it couples hydrophobic, van der Waals, and electrostatic interactions as a functional of the solvation interface. By minimizing this functional, VISM produces the solvation interface as an output of the theory. In this work, we push VISM to larger scale applications by combining it with coarse-grained solute Hamiltonians adapted from the MARTINI framework, a well-established mesoscale force modeling large-scale biomolecule assemblies. We show how MARTINI-VISM ((VISM)-V-M) compares with atomistic VISM ((VISM)-V-A) for a small set of proteins differing in size, shape, and charge distribution. We also demonstrate (VISM)-V-M's suitability to study the solvation properties of an interesting encounter complex, barnase barstar. The promising results suggest that coarse -graining the protein with the MARTINI force field is indeed a valuable step to broaden VISM's and MARTINI's applications in the near future.