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Subunit organization of the membrane-bound HIV-1 envelope glycoprotein trimer

Abstract

The trimeric human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) spike is a molecular machine that mediates virus entry into host cells and is the sole target for virus-neutralizing antibodies. The mature Env spike results from cleavage of a trimeric glycoprotein precursor, gp160, into three gp120 and three gp41 subunits. Here, we describe an ~11-Å cryo-EM structure of the trimeric HIV-1 Env precursor in its unliganded state. The three gp120 and three gp41 subunits form a cage-like structure with an interior void surrounding the trimer axis. Interprotomer contacts are limited to the gp41 transmembrane region, the torus-like gp41 ectodomain and a trimer-association domain of gp120 composed of the V1, V2 and V3 variable regions. The cage-like architecture, which is unique among characterized viral envelope proteins, restricts antibody access, reflecting requirements imposed by HIV-1 persistence in the host.

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Figure 1: The cryo-EM structure of the membrane-bound HIV-1 Env trimer at ~11-Å resolution.
Figure 2: The map segmentation of an Env protomer.
Figure 3: Fit of the crystal structure of CD4-bound gp120 core into the cryo-EM density of the unliganded Env trimer in two different configurations.
Figure 4: The gp120 trimer-association domains.
Figure 5: Architecture of gp41 trimer association.
Figure 6: Comparison of the 11-Å cryo-EM structure of the trimeric HIV-1 Env precursor with the 20-Å electron tomographic model of the native HIV-1 Env trimer on virions.

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Acknowledgements

The authors thank J. Mascola and P. Kwong (NIH Vaccine Research Center, Bethesda, Maryland, USA) and D. Burton (Scripps Institute, La Jolla, California, USA) for kindly providing antibodies; M. Ericsson, L. Trakimas and E. Benecchi for help in initial sample screening by conventional electron microscopy; D. Bell, E. Hodges and D. Wei for assistance and coordination in data collection; J. Faltskog, S. Doktor and B. Battle for laboratory coordination and assistance in building a high-performance computing system; and Y. McLaughlin and E. Carpelan for assistance in manuscript preparation. The experiments and data processing were performed in part at the Center for Nanoscale Systems at Harvard University, a member of National Nanotechnology Infrastructure Network (NNIN), which is supported by the US National Science Foundation under NSF award no. ECS-0335765. This work was funded by the US National Institutes of Health (NIH) (AI93256, AI67854 and AI24755 to J.S.), by an Innovation Award (J.S.) and a Fellowship Award (Y.M.) from the Ragon Institute of MGH, MIT and Harvard, by the International AIDS Vaccine Initiative, and by a gift from the late William F. McCarty-Cooper (J.S.).

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Y.M. and J.S. conceived this study. Y.M. designed experimental protocols; Y.M., L.W., C.G., A.H., S.-H.X., H.H., X.Y. and J.S. performed the research; Y.M. and J.S. analyzed the results and wrote the paper.

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Correspondence to Youdong Mao or Joseph Sodroski.

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Mao, Y., Wang, L., Gu, C. et al. Subunit organization of the membrane-bound HIV-1 envelope glycoprotein trimer. Nat Struct Mol Biol 19, 893–899 (2012). https://doi.org/10.1038/nsmb.2351

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