Impact of Chemical and Structural Anisotropy on the Electrophoretic Mobility of Spherical Soft Multilayer Particles: The Case of Bacteriophage MS2

Abstract

We report a theoretical investigation of the electrohydrodynamic properties of spherical soft particles composed of permeable concentric layers that differ in thickness, soft material density, chemical composition, and flow penetration degree. Starting from a recent numerical scheme developed for the computation of the direct-current electrophoretic mobility (mu) of diffuse soft bioparticles, the dependence of mu on the electrolyte concentration and solution pH is evaluated taking the known three-layered structure of bacteriophage MS2 as a supporting model system (bulk RNA, RNA-protein bound layer, and coat protein). The electrokinetic results are discussed for various layer thicknesses, hydrodynamic flow penetration degrees, and chemical compositions, and are discussed on the basis of the equilibrium electrostatic potential and hydrodynamic flow field profiles that develop within and around the structured particle. This study allows for identifying the cases where the electrophoretic mobility is a function of the inner structural and chemical specificity of the particle and not only of its outer surface properties. Along these lines, we demonstrate the general inapplicability of the notions of zeta potential (zeta) and surface charge for quantitatively interpreting electrokinetic data collected for such systems. We further shed some light on the physical meaning of the isoelectric point. In particular, numerical and analytical simulations performed on structured soft layers in indifferent electrolytic solution demonstrate that the isoelectric point is a complex ionic strength-dependent signature of the flow permeation properties and of the chemical and structural details of the particle. Finally, the electrophoretic mobilities of the MS2 virus measured at various ionic strength levels and pH values are interpreted on the basis of the theoretical formalism aforementioned. It is shown that the electrokinetic features of MS2 are to a large extent determined not only by the external proteic capsid but also by the chemical composition and hydrodynamic flow permeation of/within the inner RNA-protein bound layer and bulk RNA part of the bacteriophage. The impact of virus aggregation, as revealed by decreasing diffusion coefficients for decreasing pH values, is also discussed.

Impact of Internal RNA on Aggregation and Electrokinetics of Viruses: Comparison between MS2 Phage and Corresponding Virus-Like Particles

“…For MS2 phage, the measured IEP value (ϳ3.5 to 3.9) is lower than that expected if considering the capsid (IEP of Ͼ8) (10,15,19) only. As detailed previously (10), the dependence of electrophoretic mobility of MS2 phage on solution ionic strength is typical of that classically encountered for soft (i.e., permeable) particles.…”

“…The IEP value of viruses, which are paradigms of permeable (soft) multilayered biocells (10), is significantly impacted by their permeability to external flow (electroosmotic flow developed during the migration of the particles under the action of the externally applied field), as theoretically and experimentally demonstrated by Langlet et al (10). The IEP of soft multilayered particles is generally a complex, ionic-strength-dependent signature of the intertwined electrostatic and permeability properties of the whole particle.…”

Development and Validation of a Concentration Method for the Detection of Influenza A Viruses from Large Volumes of Surface Water

“…The adsorption of viral particles to a membrane is due to electrostatic interactions but depend on both the environmental characteristics and surface properties of the virus (20). Studies showed that charges of influenza viruses above their isoelectric point, which was approximately 5 (11, 23), were negative.…”

Electric potential profile of a spherical soft particle with a charged core

“…In the diffuse soft particle electrokinetic theory (DSPE) given by J. F. Duval [11,12], the gradual decay of the electrodynamic properties of the soft layer inside and outside the particle was considered. The extensions of the DSPE theory to multilayer soft particles have been recently done [13,14]. The inhomogeneous distribution of the charged polymer segments is demonstrated to substantially affect the overall electrokinetic response, especially in the low electrolyte concentration regime.…”