Structure and Stoichiometry of Template-Directed Recombinant HIV-1 Gag Particles

Size polydispersity of immature human immunodeficiency virus type 1 (HIV-1) particles represents a challenge for traditional methods of biological ultrastructural analysis. An in vitro model for immature HIV-1 particles constructed from recombinant Gag proteins lacking residues 16–99 and the p6 domain assembled around spherical nanoparticles functionalized with DNA. This template-directed assembly approach led to a significant reduction in size polydispersity and revealed previously unknown structural features of immature-like HIV-1 particles. Electron microscopy and image reconstruction of these particles suggest that the Gag shell formed from different protein regions that are connected by a “scar”—an extended defect connecting the edges of two continuous, regularly packed protein layers. Thus, instead of a holey protein array, the experimental model presented here appears to consist of a continuous array of ∼ 5000 proteins enveloping the core, in which regular regions are separated by extended areas of disorder.

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► Retrovirus particles are roughly spherical but are polydisperse and lack symmetry.
► We assembled particles from HIV-1 Gag protein using gold nanoparticle templates.
► Assembly on 60-nm templates sharply reduced the polydispersity of the particles.
► The protein seems to fully cover the particles, but with a “scar” in the lattice.
► The scar may reflect the difficulty of packing rod-shaped subunits on a sphere.