HIV-1 Env trimer opens through an asymmetric intermediate in which individual protomers adopt distinct conformations

Ma, Xiaochu; Lu, Maolin; Gorman, Jason; Terry, Daniel S.; Hong, Xinyu; Zhou, Zhou; Zhao, Hong; Altman, Russ B.; Arthos, James; Blanchard, Scott C.; Kwong, Peter D.; Munro, James B.; Mothes, Walther

doi:10.7554/elife.34271

Cited by 143 publications

(237 citation statements)

References 50 publications

(90 reference statements)

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“…This panel of antibodies was selected because it can distinguish "closed" versus "open" trimers. Indeed, PGT151, PG9, PGT121, and PGT126 preferentially recognize the "closed" trimer (34)(35)(36)(37), whereas CD4i Abs 17b, N12-i2, A32, and N5-i5 bind epitopes only exposed in the "open" trimer. 2G12 is an antibody that can recognize both forms of trimers (9, 37) but has a preference for the "closed" form (36).…”

Section: Resultsmentioning

confidence: 99%

Antibody-Induced Internalization of HIV-1 Env Proteins Limits Surface Expression of the Closed Conformation of Env

Anand

Grover

Tolbert

et al. 2019

J Virol

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To minimize immune responses against infected cells, HIV-1 limits the surface expression of its envelope glycoprotein (Env). Here, we demonstrate that this mechanism is specific for the Env conformation and affects the efficiency of antibody-dependent cellular cytotoxicity (ADCC). Using flow cytometry and confocal microscopy, we show that broadly neutralizing antibodies (bNAbs) targeting the "closed" conformation of Env induce its internalization from the surface. In contrast, non-neutralizing antibodies (nNAbs) are displayed on the cell surface for prolonged period of times. The bNAb-induced Env internalization can be decreased by blocking dynamin function, which translates into higher susceptibilities of infected cells to ADCC. Our results suggest that antibody-mediated Env internalization is a mechanism used by HIV-1 to evade immune responses against the "closed" conformation of Env expressed on HIV-1-infected cells.IMPORTANCE HIV-1 has evolved to acquire several strategies to limit the exposure of its envelope glycoproteins (Env) on the surface of infected cells. In this study, we show that antibody-induced Env internalization is conformation specific and reduces the susceptibility of infected cells to antibody-dependent cellular cytotoxicity (ADCC). Thus, a better understanding of this mechanism might help develop antibodies with improved capacities to mediate ADCC.

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Section: Resultsmentioning

confidence: 99%

Antibody-Induced Internalization of HIV-1 Env Proteins Limits Surface Expression of the Closed Conformation of Env

Anand

Grover

Tolbert

et al. 2019

J Virol

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“…Moreover, the acceptor fluorophore is attached through a coenzyme A "handle" with a potential contour length of over 20 Å. The smFRET data have been analyzed into three "states", with low (state 1), intermediate (state 3) and high (state 2) FRET signals, respectively [6,21,39]. Munro et al [6] reported that when Env on virion was bound with PG16 (and certain other broadly neutralizing antibodies), the low-FRET, state 1 predominated, but the same group reported recently that soluble SOSIP.664 instead gave a much higher FRET signal than did Env on virions and suggested that the SOSIP.664 structures determined by cryo-EM and x-ray crystallography do not represent the predominant conformation on the virion [21].…”

Section: Discussionmentioning

confidence: 99%

Cryo-EM structure of full-length HIV-1 Env bound with the Fab of antibody PG16

Pan¹,

Peng²,

Chen³

2019

Preprint

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The HIV-1 envelope protein (Env) is the target of neutralizing antibodies and the template for vaccine immunogen design. The dynamic conformational equilibrium of trimeric Env influences its antigenicity and potential immunogenicity. Antibodies that bind at the trimer apex stabilize a "closed" conformation characteristic of the most difficult to neutralize isolates. A goal of vaccine development is therefore to mimic the closed conformation in a designed immunogen. A disulfide-stabilized, trimeric Env ectodomain --the "SOSIP" construct --has many of the relevant properties; it is also particularly suitable for structure determination. Some singlemolecule studies have, however, suggested that the SOSIP trimer is not a good representation of Env on the surface of a virion or an infected cell. We isolated Env (fully cleaved to gp120 and gp41) from the surface of expressing cells using tagged, apex-binding Fab PG16 and determined the structure of the PG16-Env complex by cryo-EM to an overall resolution of 4.6 Å.Placing the only purification tag on the Fab ensured that the isolated Env was continuously stabilized in its closed, native conformation. The Env structure in this complex corresponds closely to the SOSIP structures determined by both x-ray crystallography and cryo-EM.Although the membrane-interacting elements are not resolved in our reconstruction, we can make inferences about the connection between ectodomain and membrane-proximal external region (MPER) by reference to the published cryo-tomography structure of an Env "spike" and the NMR structure of the MPER-transmembrane segment. We discuss these results in view of the conflicting interpretations in the literature.

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“…Due to the complexities of the triggering mechanisms for other type I systems, comparatively less is known about how they function. Perhaps the next best characterized system after HA is HIV-1 Envelope (Env) fusion glycoprotein, which is activated by two successive receptor binding events [4,75,[88][89][90][91][92]. Env first binds the CD4 receptor on the surface of T-cells which induces reorganization of the gp120 receptor binding domain and exposure of the co-receptor binding site enabling binding of either CCR5 or CXCR4 [7,92].…”

Section: Despite Their Common Architectures Activation Mechanisms Anmentioning

confidence: 99%

New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes

Benhaim

Lee

2020

Viruses

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Protein-mediated membrane fusion is a highly regulated biological process essential for cellular and organismal functions and infection by enveloped viruses. During viral entry the membrane fusion reaction is catalyzed by specialized protein machinery on the viral surface. These viral fusion proteins undergo a series of dramatic structural changes during membrane fusion where they engage, remodel, and ultimately fuse with the host membrane. The structural and dynamic nature of these conformational changes and their impact on the membranes have long-eluded characterization. Recent advances in structural and biophysical methodologies have enabled researchers to directly observe viral fusion proteins as they carry out their functions during membrane fusion. Here we review the structure and function of type I viral fusion proteins and mechanisms of protein-mediated membrane fusion. We highlight how recent technological advances and new biophysical approaches are providing unprecedented new insight into the membrane fusion reaction.Viruses 2020, 12, 413 2 of 21 built. Type II fusion proteins are found in viruses including flaviviruses and alphaviruses such as Dengue, Zika, and Chikungunya viruses, and even have been identified in eukaryotic cell-cell fusion systems [9][10][11][12]. Type III fusion proteins are found in rhabdoviruses (such as Rabies and Vesicular Stomatatis virus G glycoproteins), herpesviruses (Herpes Simplex virus 1 gB protein), as well as baculovirus [12][13][14][15][16]. While the individual folds exhibited by these classes are completely different, they share common functional traits in that all adopt a pre-fusion conformation prior to activation in which one terminus of the protein is anchored in the virus membrane by a transmembrane domain and a second membrane active component, either a fusion peptide or loop, is sequestered from interacting with membranes ( Figure 1) [12]. A trigger or set of triggers, such as exposure to low pH in endosomes or receptor binding, spurs the machinery to reorganize into a post-fusion state in which the two membrane active components are colocalized.Until recently, static structures of the pre-and post-fusion states of isolated fusion protein ectodomains and biochemical or spectroscopic measurements were the primary pieces of information that informed our models of membrane fusion. While the static structures provide defined endpoints for the conformational change that drives membrane fusion, they do not tell us how these conformational changes occur or how these proteins interact with and perturb the lipid membrane during fusion. Likewise, fluorescence spectroscopy and circular dichroism studies have shown that HA-fusion activation leads to population of discernable intermediates rather than transitioning directly and irreversibly from pre-to post-fusion states [17][18][19][20]. These studies show that not all HAs respond to activation in the same way and some require different pH conditions to fully activate [20]. While such studies provided valuable information...

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HIV-1 Env trimer opens through an asymmetric intermediate in which individual protomers adopt distinct conformations

Cited by 143 publications

References 50 publications

Antibody-Induced Internalization of HIV-1 Env Proteins Limits Surface Expression of the Closed Conformation of Env

Antibody-Induced Internalization of HIV-1 Env Proteins Limits Surface Expression of the Closed Conformation of Env

Cryo-EM structure of full-length HIV-1 Env bound with the Fab of antibody PG16

New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes

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