The encapsulation of polyanions by virus coat proteins, whether single-stranded RNAs or synthetic polymers, is primarily driven by attractive electrostatic interactions between the positively charged, structurally disordered RNA binding domains of the virus coat proteins and the negatively charged polyanions. Theoretically, this interaction is often modeled by coarse-graining the charge distribution of the binding domains, either by projecting the charges onto the inner surface of the protein shell or by spreading them across a region representing the capsid lumen where the binding domains are located. In practice, however, the positive charges are not uniformly distributed across the binding domains, which themselves are positioned at discrete, specific sites on the shell surface. Here, we use molecular dynamics simulations to investigate the impact of localized interactions on the most probable or optimal length of the encapsulated polymer, revealing that the specific location of charges along the binding domains plays a significant role, consistent with experimental observations. Comparing the simulations with predictions from a simple mean-field theory taken from the literature, we find that while the general trends are reasonably well captured, quantitative discrepancies arise between the two approaches.

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• Applications of soft matter
• Developmental biology
• Physics of computation