Electrostatic Theory of the Acidity of the Solution in the Lumina of Viruses and Virus-Like Particles

Abstract

Recently, Maassen et al. measured an appreciable pH difference between the bulk solution and the solution in the lumen of virus-like particles, self-assembled in an aqueous buffer solution containing the coat proteins of a simple plant virus and polyanions (Maassen, S. J.; et al. Small 2018, 14, 1802081). They attribute this to the Donnan effect, caused by an imbalance between the number of negative charges on the encapsulated polyelectrolyte molecules and the number of positive charges on the RNA binding domains of the coat proteins that make up the virus shell or capsid. By applying Poisson–Boltzmann theory, we confirm this conclusion and show that simple Donnan theory is accurate even for the smallest of viruses and virus-like particles. This, in part, is due to the additional screening caused by the presence of a large number of immobile charges in the cavity of the shell. The presence of a net charge on the outer surface of the capsid we find in practice to not have a large effect on the pH shift. Hence, Donnan theory can indeed be applied to connect the local pH and the amount of encapsulated material. The large shifts up to a full pH unit that we predict must have consequences for applications of virus capsids as nanocontainers in bionanotechnology and artificial cell organelles.

Conditional existence of Donnan potential in soft particles and surfaces: Dependence on steric effects mediated by electrolyte ions and structural charges

“…Given the importance of Donnan theory for the electrostatics and electrokinetics of soft particles and soft macroscopic surfaces [62][63][64], the current work may be valuable to address the domain of validity of this theory, especially for biological particles under high salt concentration conditions where steric effects can be significant. In another context, binding of metal ions and protons to particulate organic matter is commonly evaluated by equilibrium Non-Ideal Competitive Adsorption (NICA)-Donnan model [65].…”

Virus-like particles nanoreactors: from catalysis towards bio-applications

“…In a recent development, Muhren et al confirmed the applicability of the Donnan theory in predicting the local pH shift through the utilization of the Poisson-Boltzmann theory. 114 Both theoretical analyses and experimental studies suggest that the immobile charges of amino acid residues on the surface of capsid can induce an imbalanced charge distribution. This disparity could potentially influence the influx of positively charged protons, consequently leading to pH shifts.…”

“…107,112 In addition to the studies of pH in native VLPs, a comprehensive understanding of the physicochemical condition and personalized regulation of the local pH within viral capsids holds the potential to position VLPs as promising platforms for enhancing catalytic performance. 107,114…”