<scp>SNARE</scp>‐mediated membrane fusion is a two‐stage process driven by entropic forces

McDargh, Zachary A.; Polley, Anirban; O’Shaughnessy, Ben

doi:10.1002/1873-3468.13277

Cited by 17 publications

(12 citation statements)

References 63 publications

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“…The contact zone then expands to form an extended, tightly docked interface between the two outer membrane leaflets ( Figure 4A,B). Similar extended interface contacts have been observed during SNARE protein-mediated membrane fusion and the GTP-dependent alastin fusion protein [2,34,[133][134][135][136][137]. Higher levels of cholesterol or inclusion of lipids found in mature endosomes in the target membrane were found to promote formation of these extended interfaces [115].…”

Section: Visualizing Viral Membrane Fusion In Actionsupporting

confidence: 63%

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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Section: Visualizing Viral Membrane Fusion In Actionsupporting

confidence: 63%

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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“…Similarly, cell fusion assays using nanodiscs, synthetic lipoprotein particles that contain a small (∼17 nm diameter) circular lipid bilayer with differing numbers of SNAREs, suggested two SNARE complexes were required to open a fusion pore, but seven SNARE complexes were required to fully dilate the pore (Shi et al, 2012). This number of SNARE complexes required for fusion was consistent with predictions from the Karatekin and O'Shaughnessy lab supporting their biophysical model of SNAREpin repulsion as an explanation for fusion pore expansion (McDargh et al, 2018).…”

Section: Models Of Formationsupporting

confidence: 79%

SNARE-Mediated Exocytosis in Neuronal Development

Urbina

Gupton

2020

Front. Mol. Neurosci.

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The formation of the nervous system involves establishing complex networks of synaptic connections between proper partners. This developmental undertaking requires the rapid expansion of the plasma membrane surface area as neurons grow and polarize, extending axons through the extracellular environment. Critical to the expansion of the plasma membrane and addition of plasma membrane material is exocytic vesicle fusion, a regulated mechanism driven by soluble N-ethylmaleimide-sensitive factor attachment proteins receptors (SNAREs). Since their discovery, SNAREs have been implicated in several critical neuronal functions involving exocytic fusion in addition to synaptic transmission, including neurite initiation and outgrowth, axon specification, axon extension, and synaptogenesis. Decades of research have uncovered a rich variety of SNARE expression and function. The basis of SNARE-mediated fusion, the opening of a fusion pore, remains an enigmatic event, despite an incredible amount of research, as fusion is not only heterogeneous but also spatially small and temporally fast. Multiple modes of exocytosis have been proposed, with full-vesicle fusion (FFV) and kiss-and-run (KNR) being the best described. Whereas most in vitro work has reconstituted fusion using VAMP-2, SNAP-25, and syntaxin-1; there is much to learn regarding the behaviors of distinct SNARE complexes. In the past few years, robust heterogeneity in the kinetics and fate of the fusion pore that varies by cell type have been uncovered, suggesting a paradigm shift in how the modes of exocytosis are viewed is warranted. Here, we explore both classic and recent work uncovering the variety of SNAREs and their importance in the development of neurons, as well as historical and newly proposed modes of exocytosis, their regulation, and proteins involved in the regulation of fusion kinetics.

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“…While attention has been focused in previous studies on the proteins involved in the entry process (4,(8)(9)(10), much less is known of the roles played by the lipids involved despite inter-membrane lipid mixing being central to membrane fusion. Lipid mixing may be an important barrier to fusion given that the lipidomes of the HIV-1 and target cell membranes are vastly different (11).…”

Section: Introductionmentioning

confidence: 99%

Concerted interactions between multiple gp41 trimers and the target cell lipidome may be required for HIV-1 entry

Gorai

Sahoo

Srivastava

et al. 2020

Preprint

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The HIV-1 envelope glycoprotein gp41 mediates the fusion between viral and host cell membranes leading to virus entry and target cell infection. Despite years of research, important aspects of this process such as the number of gp41 trimers involved and how they orchestrate the rearrangement of the lipids in the apposed membranes along the fusion pathway remain obscure. To elucidate these molecular underpinnings, we performed coarse-grained molecular dynamics simulations of HIV-1 virions pinned to the CD4 T cell membrane by different numbers of gp41 trimers. We built realistic cell and viral membranes by mimicking their respective lipid compositions. We found that a single gp41 was inadequate for mediating fusion. Lipid mixing between membranes, indicating the onset of fusion, was efficient when 3 or more gp41 trimers pinned the membranes. The gp41 trimers interacted strongly with many different lipids in the host cell membrane, triggering lipid configurational rearrangements, exchange, and mixing. Simpler membranes, comprising fewer lipid types, displayed strong resistance to fusion, revealing the crucial role of the lipidomes in HIV-1 entry. Performing simulations at different temperatures, we estimated the free energy barrier to lipid mixing, and hence membrane stalk formation, with 4 tethering gp41 trimers to be ∼6.2 kcal/mol, a >4-fold reduction over estimates without gp41. Together, these findings present molecular-level, quantitative insights into the early stages of gp41-mediated HIV-1 entry. Preventing the requisite gp41 molecules from tethering the membranes or altering membrane lipid compositions may be potential intervention strategies. SIGNIFICANCEInteractions between viral envelope proteins and host cell surface receptors leading to HIV-1 entry are well studied, however the role of membrane lipids remains obscure, although entry hinges on lipid mixing and the fusion of viral and cell membranes. We performed detailed simulations of HIV-1 and target cell membranes tethered by viral gp41 trimeric proteins to elucidate the proteo-lipidic contributions to viral entry. We found that the cooperative effects of multiple gp41 trimers and natural lipidomes of the membranes facilitate membrane fusion. The functional domains of gp41 altered local lipid concentrations, reduced membrane repulsions, and facilitated inter-membrane lipid mixing. These molecular-level insights offer a glimpse of the cryptic mechanisms underlying HIV-1 entry and suggest new interventions to combat HIV-1 infection.

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SNARE‐mediated membrane fusion is a two‐stage process driven by entropic forces

Cited by 17 publications

References 63 publications

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

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

SNARE-Mediated Exocytosis in Neuronal Development

Concerted interactions between multiple gp41 trimers and the target cell lipidome may be required for HIV-1 entry

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