Programmable Polymorphism of a Virus-Like Particle

Abstract

Virus-like particles (VLPs) have significant potential as both artificial vaccines and drug delivery systems. The ability to control their size has wide ranging utility, but achieving such controlled polymorphism using a single protein subunit is challenging as it requires altering VLP geometry. Here we achieve size control of MS2 bacteriophage VLPs via insertion of amino acid sequences in an external loop to shift its morphology to significantly larger forms. The resulting VLP size and geometry is controlled by altering the length and type of the insert used. Cryo-EM structures of the new VLPs, in combination with a kinetic model of their assembly, show that the abundance of wild type (T=3), T=4, D3 and D5 symmetrical VLPs can be controlled in this way. We propose a mechanism whereby the insert leads to a change in the dynamic behavior of the capsid protein dimer, affecting the interconversion between the symmetric and asymmetric conformers and thus determining VLP size and morphology.

Multiscale Modeling of Hepatitis B Virus Capsid Assembly and its Dimorphism

“…These results are also consistent with recent suggestions that coupling between conformational interconversion and interaction strengths provides an important means of regulatory control over the timing and robustness of assembly [112, 134, 140, 141]. Moreover, Biela et al [142] recently demonstrated that assembly of larger capsids from MS2 capsids ( T =4 and D5) could be achieved by engineering insertions into the capsid protein that likely shift the capsid protein conformational equilibrium (analogous to changing our parameter ).…”

“…These results are also consistent with recent suggestions that coupling between conformational interconversion and interaction strengths provides an important means of regulatory control over the timing and robustness of assembly [112,134,140,141]. Moreover, Biela et al [142] recently demonstrated that assembly of larger capsids from MS2 capsids (T =4 and D5) could be achieved by engineering insertions into the capsid protein that likely shift the capsid protein conformational equilibrium (analogous to changing our parameter ∆g conf CD → AB ). The need for conformational specificity when accounting for HBV material properties sheds new light on previous results for a model of icosahedral capsid assembly with only one subunit species, which found that much higher values of the bending modulus, corresponding to much smaller values of the Foppl von Karman number (FvK < 0.25, compared to FvK ≈ 500 for HBV), were required to observe assembly into T =4 structures [91,143].…”

The diversity of protein-protein interaction interfaces within T=3 icosahedral viral capsids

“…Similar studies have also been performed with T = 3 jelly-roll capsids (Ren et al, 2006;Barnhill et al, 2007;Lockney et al, 2011;Yildiz et al, 2012;Zeng et al, 2013;Sokullu et al, 2019;Durán-Meza et al, 2020). Understanding protein-protein interactions is an important step in improvising such systems, as was shown in a recent study on MS2 (Biela et al, 2022), where insertions were made to tweak the dimerization interface, allowing the formation of larger capsid structures.…”