Unclosed HIV-1 Capsids Suggest a Curled Sheet Model of Assembly

• Published in: Journal of molecular biology 2013-01, Vol.425 (1), p.112-123
• Main Authors: Yu, Zhiheng, Dobro, Megan J., Woodward, Cora L., Levandovsky, Artem, Danielson, Cindy M., Sandrin, Virginie, Shi, Jiong, Aiken, Christopher, Zandi, Roya, Hope, Thomas J., Jensen, Grant J.
• Format: Article
• Language: English
• Subjects: Animals; capsid; Capsid - chemistry; Carrier Proteins - chemistry; coat proteins; Computer Simulation; Cryoelectron Microscopy; cryotomography; Equine infectious anemia virus; genome; green fluorescent protein; Green Fluorescent Proteins; HEK293 Cells; HIV-1; HIV-1 - chemistry; HIV-1 - physiology; Human immunodeficiency virus 1; Humans; image analysis; Infectious Anemia Virus, Equine - chemistry; Infectious Anemia Virus, Equine - physiology; Microscopy, Fluorescence; Models, Molecular; Retrovirus; retroviruses; RNA; Viral Core Proteins - chemistry; Virus Assembly
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2012.10.006

The RNA genome of retroviruses is encased within a protein capsid. To gather insight into the assembly and function of this capsid, we used electron cryotomography to image human immunodeficiency virus (HIV) and equine infectious anemia virus (EIAV) particles. While the majority of viral cores appeared closed, a variety of unclosed structures including rolled sheets, extra flaps, and cores with holes in the tip were also seen. Simulations of nonequilibrium growth of elastic sheets recapitulated each of these aberrations and further predicted the occasional presence of seams, for which tentative evidence was also found within the cryotomograms. To test the integrity of viral capsids in vivo, we observed that ~25% of cytoplasmic HIV complexes captured by TRIM5α had holes large enough to allow internal green fluorescent protein (GFP) molecules to escape. Together, these findings suggest that HIV assembly at least sometimes involves the union in space of two edges of a curling sheet and results in a substantial number of unclosed forms. [Display omitted] ► Retroviruses undergo a capsid assembly process of unknown mechanism. ► Cryotomography revealed that some capsids fail to close, exhibiting holes and seams. ► Invivo fluorescence images confirm that some capsids have holes large enough to leak green fluorescent protein. ► Simulations of nonequilibrium growth of elastic sheets recapitulate each aberration. ► We suggest a new pathway for HIV capsid assembly involving a curled sheet model.