Salt Enhances the Thermostability of Enteroviruses by Stabilizing Capsid Protein Interfaces

Abstract

Enteroviruses are common agents of infectious disease that are spread by the fecal-oral route. They are readily inactivated by mild heat, which causes the viral capsid to disintegrate or undergo conformational change. While beneficial for the thermal treatment of food or water, this heat sensitivity poses challenges for the stability of enterovirus vaccines. The thermostability of an enterovirus can be modulated by the composition of the suspending matrix, though the effects of the matrix on virus stability are not understood. Here, we determined the thermostability of four enterovirus strains in solutions with various concentrations of NaCl and different pH values. The experimental findings were combined with molecular modeling of the protein interaction forces at the pentamer and the protomer interfaces of the viral capsids. While pH only had a modest effect on thermostability, increasing NaCl concentrations raised the breakpoint temperatures of all viruses tested by up to 20°C. This breakpoint shift could be explained by an enhancement of the van der Waals attraction forces at the two protein interfaces. In comparison, the (net repulsive) electrostatic interactions were less affected by NaCl. Depending on the interface considered, the breakpoint temperature shifted by 7.5 or 5.6°C per 100-kcal/(mol·Å) increase in protein interaction force. IMPORTANCE The genus Enterovirus encompasses important contaminants of water and food (e.g., coxsackieviruses), as well as viruses of acute public health concern (e.g., poliovirus). Depending on the properties of the surrounding matrix, enteroviruses exhibit different sensitivities to heat, which in turn influences their persistence in the environment, during food treatment, and during vaccine storage. Here, we determined the effect of NaCl and pH on the heat stability of different enteroviruses and related the observed effects to changes in protein interaction forces in the viral capsid. We demonstrate that NaCl renders enteroviruses thermotolerant and that this effect stems from an increase in van der Waals forces at different protein subunits in the viral capsid. This work sheds light on the mechanism by which salt enhances virus stability.

The spectrum of building block conformers sustains the biophysical properties of clinically-oriented self-assembling protein nanoparticles

“…This finding was indicative that forces other than divalent cation coordination were supporting the organization of such a more complex material. For other types of related protein-only NPs, hydrogen bonds, van der Waals and especially electrostatic interactions were predicted to act, promoting and maintaining protein-protein contacts [23], in a similar way in which monomers are kept together in viral capsids [43][44][45]. In this context, the addition of 0.5% Triton X-100 reduced the size of the materials from more than 100 nm (mean) to 10 nm (Fig.…”

Stability of SARS-CoV-2 in cold-chain transportation environments and the efficacy of disinfection measures

“…we demonstrated that cold-chain temperature protects SARS-CoV-2 pseudovirus survival for a long time and decreases the decay rate of the virus compared to exposure in vitro under room temperature. Seawater did not decrease the decay of SARS-CoV-2 pseudovirus in vitro at -18° C, but protected the survival and enhanced the thermostability of SARS-CoV-2 pseudovirus in vitro under the condition of the repeated freeze-thawing cycle, Researchers have shown that salt enhances the thermostability of viruses by increasing van der Waals force and decreasing repulsive electrostatic force (CRAIG WALLIS; Meister et al, 2020; MELNICK)., and could enhance the risk of the SARS-CoV-2 transmission.…”

Stability of SARS-CoV-2 in cold-chain transportation environments and the efficacy of disinfection measures

“…The results of freeze−thaw experiments suggest that salt ions in seawater can slow the decay rate of SARS-CoV-2 pseudovirus, but the specific reasons need to be further studied. Researchers have shown that salt enhances the thermostability of viruses by increasing van der Waals forces( Meister et al., 2020 ). Although SARS-CoV-2, with a lipid envelope, is more tolerant to low temperatures than viruses without an envelope ( Yao et al., 2020 ; Isachenko et al., 2021 ), it still can freeze.…”