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. 2013 Sep;87(17):9865-72.
doi: 10.1128/JVI.01222-13. Epub 2013 Jul 3.

Structural Characterization of Cleaved, Soluble HIV-1 Envelope Glycoprotein Trimers

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Free PMC article

Structural Characterization of Cleaved, Soluble HIV-1 Envelope Glycoprotein Trimers

Reza Khayat et al. J Virol. .
Free PMC article

Abstract

Human immunodeficiency virus type 1 (HIV-1) infection is a significant global public health problem for which development of an effective prophylactic vaccine remains a high scientific priority. Many concepts for a vaccine are focused on induction of appropriate titers of broadly neutralizing antibodies (bNAbs) against the viral envelope (Env) glycoproteins gp120 and gp41, but no immunogen has yet accomplished this goal in animals or humans. One approach to induction of bNAbs is to design soluble, trimeric mimics of the native viral Env trimer. Here, we describe structural studies by negative-stain electron microscopy of several variants of soluble Env trimers based on the KNH1144 subtype A sequence. These Env trimers are fully cleaved between the gp120 and gp41 components and stabilized by specific amino acid substitutions. We also illustrate the structural consequences of deletion of the V1/V2 and V3 variable loops from gp120 and the membrane-proximal external region (MPER) from gp41. All of these variants adopt a trimeric configuration that appropriately mimics native Env spikes, including the CD4 receptor-binding site and the epitope for the VRC PG04 bNAb. These cleaved, soluble trimer designs can be adapted for use with multiple different env genes for both vaccine and structural studies.

Figures

Fig 1
Fig 1
Schematic representation of the SOSIP constructs used in this study. The gp120 constant domains are labeled C1 to C5, while the variable loops are labeled V1 to V5. A disulfide bond (SOS) stabilizes the gp120-gp41 interaction. The fusion peptide is labeled FP, while the heptad repeat 1 (HR1), heptad repeat 2 (HR2), and the membrane-proximal region (MPER) are also indicated.
Fig 2
Fig 2
Comparison of SOSIP constructs to HIV-decorated Env trimers. Shown is the surface representation of the SOSIP image reconstructions compared to the published HIV-1 surface Env trimers. (Top view) Looking down the 3-fold axis of each trimer (with the viral membrane in the distance). (Side view) Looking parallel to the viral membrane at the bottom of the figure. (A) Unliganded HIV-1 BaL (EMD-5022); (B) SOSIP.681 filtered to 25-Å resolution; (C) HIV-1 BaL liganded to sCD4 (EMD-5455); (D) SOSIP.681 liganded to sCD4 filtered to 25-Å resolution; (E) HIV-1 BaL liganded to VRC03 (EMD-5458); (F) SOSIP.681 liganded to VRC PG04 filtered to 15-Å resolution. Labeled are the body, waist, and stem of the SOSIP.681 image reconstructions (see the text).
Fig 3
Fig 3
Comparison of SOSIP image reconstructions. Shown is the surface representation of image reconstructions for the various liganded and unliganded SOSIP.681 and SOSIP.664 low-pass filtered to 22-Å resolution. Shown are the top and side views of (A) SOSIP.681, (B) SOSIP.681.ΔV1V2V3, (C) SOSIP.681 liganded to VRC PG04, (D) SOSIP.681.ΔV1V2V3 liganded to VRC PG04, (E) SOSIP.681 liganded to sCD4, (F) SOSIP.664, (G) SOSIP.664 liganded to VRC PG04, (H) SOSIP.664.ΔV1V2V3 liganded to VRC PG04, (I) SOSIP.664 liganded to sCD4, and (J) SOSIP.664.ΔV1V2V3 liganded to sCD4.
Fig 4
Fig 4
Comparison of segmented SOSIP image reconstructions. Surface representation of image reconstructions segmented using the docked crystal structures of gp120core, V1/V2 and V3 loops, gp120core liganded to VRC PG04, and gp120core liganded to sCD4. The image layout is identical to Fig. 3. The coloring is as follows: gp120core, cyan; V1/V2, yellow; V3, green; VRC PG04 heavy chain, blue; VRC PG04 light chain, white; and gp41 and termini of gp120, gray. See Materials and Methods for details.

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