Lowered pH Leads to Fusion Peptide Release and a Highly Dynamic Intermediate of Influenza Hemagglutinin

Lin, Xin; Noel, Jeffrey K.; Wang, Qinghua; Ma, Jianpeng; Onuchic, José N.

doi:10.1021/acs.jpcb.6b06775

Cited by 13 publications

(12 citation statements)

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“…Time-resolved pH-jump experiments on membrane-bound proteins show great promise for capturing these conformational changes in HA (53). A slower transition of the B loop and a long-lived intermediate may provide functional benefits by providing additional free-energy drive for membrane fusion and contributing extra time to the association among multiple HAs (54). We can speculate that this intermediate state is followed by the final rearrangement of S4 and S5, providing sufficient free energy to stabilize the final structure and possibly bringing the viral and cell membranes together.…”

Section: Discussionmentioning

confidence: 99%

“…An important consideration for the HA 2 rearrangement is its pH sensitivity. Several regions of HA are suggested to respond to lowered pH, including dissociation of HA 1 (59), destabilization of the fusion peptide burial pocket (54,60), and stability of the B-loop trimeric coiled coil (5). Interestingly, isolated HA 2 folds into the postfusion structure at both neutral and low pH (61), suggesting a limited role for pH in HA 2 .…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Atomistic simulations indicate the functional loop-to-coiled-coil transition in influenza hemagglutinin is not downhill

Lin

Noel

Wang

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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Influenza hemagglutinin (HA) mediates viral entry into host cells through a large-scale conformational rearrangement at low pH that leads to fusion of the viral and endosomal membranes. Crystallographic and biochemical data suggest that a loop-to-coiled-coil transition of the B-loop region of HA is important for driving this structural rearrangement. However, the microscopic picture for this proposed "spring-loaded" movement is missing. In this study, we focus on understanding the transition of the B loop and perform a set of all-atom molecular dynamics simulations of the full B-loop trimeric structure with the CHARMM36 force field. The free-energy profile constructed from our simulations describes a B loop that stably folds half of the postfusion coiled coil in tens of microseconds, but the full coiled coil is unfavorable. A buried hydrophilic residue, Thr59, is implicated in destabilizing the coiled coil. Interestingly, this conserved threonine is the only residue in the B loop that strictly differentiates between the group 1 and 2 HA molecules. Microsecond-scale constant temperature simulations revealed that kinetic traps in the structural switch of the B loop can be caused by nonnative, intramonomer, or intermonomer β-sheets. The addition of the A helix stabilized the postfusion state of the B loop, but introduced the possibility for further β-sheet structures. Overall, our results do not support a description of the B loop in group 2 HAs as a stiff spring, but, rather, it allows for more structural heterogeneity in the placement of the fusion peptides during the fusion process.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Atomistic simulations indicate the functional loop-to-coiled-coil transition in influenza hemagglutinin is not downhill

Lin

Noel

Wang

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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“…The authors concluded that at increasingly acidic condition, prior to activation, HA becomes primed for fusion peptide release, adding further support to this emerging mechanistic model. These recent studies suggest that in the early stages of fusion activation HA adopts a dynamic fusion-peptide-released intermediate state [22,27,33,80,81,[84][85][86][87].…”

Section: Despite Their Common Architectures Activation Mechanisms Anmentioning

confidence: 95%

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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“…The "uncaging" model for HA activation suggests that HA1 acts as a cage or clamp containing the spring-loaded HA2 fusion machine; whereupon low pH releases the HA1 cage, allowing rapid and irreversible activation of the spring-loaded HA2 fusion machine (7,(11)(12)(13). By contrast, a "fusion peptide release" model suggests that low pH first stimulates the release of the HA2 N-terminal fusion peptide hook from its sequestered pocket in the core of HA2 before HA1 head domains dissociating from each other (12,(14)(15)(16)(17)(18)(19)(20)(21). In this model, the exposed fusion peptide, tethered to a highly dynamic HA2 subunit, is deployed and available to engage with the target membrane before the large-scale refolding of HA2 into the postfusion, hairpin conformation (22).…”

Section: Introductionmentioning

confidence: 99%

Structural monitoring of a transient intermediate in the hemagglutinin fusion machinery on influenza virions

et al. 2020

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The influenza virus hemagglutinin (HA) fusion protein has long been viewed as a “spring-loaded” fusion machine whereby activation at low pH initiates a rapid and irreversible cascade of conformational changes that drives the membrane fusion reaction. This mechanism has shaped our understanding of how type 1 viral fusion proteins function as a whole. Experimental limitations have hindered efforts to expand our mechanistic and structural understanding of viral membrane fusion. Here, we used pulse-labeling hydrogen/deuterium exchange mass spectrometry and cryo–electron tomography to monitor and characterize the structural dynamics of HA during fusion activation on intact virions. Our data reveal how concurrent reorganizations at the HA1 receptor binding domain interface and HA2 fusion subunit produce a dynamic fusion intermediate ensemble in full-length HA. The soluble HA ectodomain transitions directly to the postfusion state with no observable intermediate.

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Lowered pH Leads to Fusion Peptide Release and a Highly Dynamic Intermediate of Influenza Hemagglutinin

Cited by 13 publications

References 50 publications

Atomistic simulations indicate the functional loop-to-coiled-coil transition in influenza hemagglutinin is not downhill

Atomistic simulations indicate the functional loop-to-coiled-coil transition in influenza hemagglutinin is not downhill

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

Structural monitoring of a transient intermediate in the hemagglutinin fusion machinery on influenza virions

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