Article
- The EMBO Journal (2007) 26, 2218 - 2226
- doi:10.1038/sj.emboj.7601664
Published online: 29 March 2007
Subject Categories:
Electron cryotomography of immature HIV-1 virions reveals the structure of the CA and SP1 Gag shells
Elizabeth R Wright1,a, Jordan B Schooler1,a, H Jane Ding1, Collin Kieffer2, Christopher Fillmore2, Wesley I Sundquist2 and Grant J Jensen1
- Division of Biology, California Institute of Technology, Pasadena, CA, USA
- Department of Biochemistry, University of Utah, Salt Lake City, UT, USA
Correspondence to:
Grant J Jensen, Division of Biology, California Institute of Technology, 1200 East California Blvd., MC: 114-96, Pasadena, CA 91125 USA. Tel.: +1 626 395 8827; Fax: +1 626 395 5730; E-mail: jensen@caltech.edu
aThese authors contributed equally to this work
Received 3 January 2007; Accepted 5 March 2007
Abstract
The major structural elements of retroviruses are contained in a single polyprotein, Gag, which in human immunodeficiency virus type 1 (HIV-1) comprises the MA, CA, spacer peptide 1 (SP1), NC, SP2, and p6 polypeptides. In the immature HIV-1 virion, the domains of Gag are arranged radially with the N-terminal MA domain at the membrane and C-terminal NC-SP2-p6 region nearest to the center. Here, we report the three-dimensional structures of individual immature HIV-1 virions, as obtained by electron cryotomography. The concentric shells of the Gag polyprotein are clearly visible, and radial projections of the different Gag layers reveal patches of hexagonal order within the CA and SP1 shells. Averaging well-ordered unit cells leads to a model in which each CA hexamer is stabilized by a bundle of six SP1 helices. This model suggests why the SP1 spacer is essential for assembly of the Gag lattice and how cleavage between SP1 and CA acts as a structural switch controlling maturation.
Keywords:
- electron cryotomography,
- Gag,
- human immunodeficiency virus type 1 (HIV-1),
- spacer peptide 1 (SP1)
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