Electrophoretic Mobilities of a Viral Capsid, Its Capsid Protein, and Their Relation to Viral Assembly

Abstract

The self-assembly of many viral capsids is dominated by protein-protein electrostatic interactions. To have a better understanding of this process, it is important to know how the protein and the capsid surface charges vary as a function of the pH and ionic strength. In this work, using phase analysis light scattering, we measured the electrophoretic mobility (EM) of the cowpea chlorotic mottle virus (CCMV), its capsid protein (CP), and a cleaved CP that lacks its basic terminus, as a function of pH and ionic strength. The EM measurements of the CP are difficult to carry out due to its tendency to self-assemble into capsids; we show how to circumvent this problem by appropriately changing the CP concentration. We found that the isoelectric points (pIs) of the virion and of the CP are insensitive to ionic strength. The onset of multishell structures in the phase diagram of the CCMV CP as a function of ionic strength and pH (and its absence in the brome mosaic virus (BMV) CP phase diagram) can be related to the pI of the capsid. We propose that the transition from multiwall shells to nanotube structures is due to a change in the spontaneous curvature of the CP at its pI. A nonzero limit of the EM at high ionic strength is characteristic of a soft colloid, but a near identity of the EMs of empty capsids and those containing RNA indicates that the EM reflects only the charge distribution in the CP. The Henry equation has been used to provide approximate values of the capsid surface charge as a function of pH and I.

Oligonucleotide Length‐Dependent Formation of Virus‐Like Particles

“…This binding results from electrostatic attraction of the negatively charged cargo and the positively charged arginine‐rich motif (ARM) on the N terminus of CCMV. In the case of CCMV, this interaction is known to be independent of pH, within the stability range of the virus, but it depends strongly on the ionic strength of the solution . The combination of CP–CP and CP–cargo interactions drive assembly to make it more efficient at acidic pH and less efficient at neutral pH .…”

Weighing Polyelectrolytes Packaged in Viruslike Particles

“…Lastly, the different values of hM p i=hM cap i at different pD emphasize the importance of the capsomer self-energy entering the total free energy. A higher pD increases the capsomer self-energy through the ionization of carboxylate groups which thus enhances the electrostatic repulsion between capsomers [25]. This causes the capsids to swell and to package a larger amount of polyelectrolyte in such a way that the mass ratio increases.…”

Plant-based porcine reproductive and respiratory syndrome virus VLPs induce an immune response in mice

“…These changes in the way this capsid protein selfassemble are due to changes in the spontaneous curvature of the capsid protein leading to destabilization of pentamers in favor of hexamers, due to changes in protein charges as a function of pH; pentamers are required for the formation of spherical capsids, therefore this will result in the formation of elongated instead of spherical capsids (Vega-Acosta et al, 2014). In this work, we also observed an increase in the VLPs size which occurred when…”