We (in collaboration with Ariella Oppenheim) showed that slow dialysis, over several hours, of wild-type Simian Virus 40 (wt SV40) against salt solutions containing MgCl2, with or without added NaCl, resulted in wt SV40 that are arranged in a body cubic center crystal structure with Im3m space group, in coexistence with soluble wt SV40 nanoparticles. The crystals formed above a critical MgCl2 concentrations. Reentrant melting and resolubilization of the virus particles took place when the MgCl2 concentrations passed a second threshold. Using synchrotron solution X-ray scattering we determined the mass fraction of the soluble and crystal phases as a function of MgCl2 and NaCl concentrations. A thermodynamic model, which balances the chemical potentials of the Mg2+ ions in each of the possible states, explained our observations. The model reveals the mechanism of both the crystallization and the reentrant melting and resolubilization and shows that counterion entropy is the main driving force for both processes (ACS Nano 2017).
Calcium ions and disulfide bonds are involved in the stabilization of the capsid of wt SV40 and are playing a role in its assembly and disassembly pathways. We showed that the volume of wt SV40 or SV40-like particles swell when both of their calcium ions are chelated by ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) and its disulfide bonds are reduced by dithiothreitol (DTT) (ACS Omega 2019).
