Role of polyion length in the co-assembly of stoichiometric viral-like nanoparticles

To study the polyion-driven assembly of an icosahedral T = 1 capsid model when the polyion charge matches that of the capsid, coarse-grained molecular dynamics computer simulations were performed. A bonded interaction was considered to take into account the elasticity of the capsomers, the capsid building blocks, and an adjusted Lennard-Jones non-bonded interaction strength parameter was used for an optimized capsid formation. The process was presented in terms of co-assembly kinetics and analyzed using the time evolution of polyion-capsomer and capsomer-capsomer clusters, as well as the size and small-angle scattering intensity of the oppositely charged complex. Simulations containing systems with constant electrostatic coupling between polyion and capsomers showed that the capsid formation implied one nucleus for short polyions, and two nuclei with polyion acting as a tether otherwise. Simulations carried out at increasing electrostatic coupling revealed that the polyion whose contour length exceeded pronouncedly the capsid size could be encapsulated due to the fact that the capsid nucleation mirrored the polyion collapse at the stoichiometric charge ratio and that a rejection-rebinding mechanism for relaxing the kinetically-trapped complex states was provided. This relaxation mechanism vanished when the polyion could capture an increased number of capsomers, case in which the polyion accommodated in connected incomplete capsids.