1
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Lin Y, Exell J, Lin H, Zhang C, Welsher KD. Hour-Long, Kilohertz Sampling Rate Three-Dimensional Single-Virus Tracking in Live Cells Enabled by StayGold Fluorescent Protein Fusions. J Phys Chem B 2024; 128:5590-5600. [PMID: 38808440 DOI: 10.1021/acs.jpcb.4c01710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
A viral infection process covers a large range of spatiotemporal scales. Tracking the viral infection process with fluorescent labels over long durations while maintaining a fast sampling rate requires bright and highly photostable labels. StayGold is a recently identified green fluorescent protein that has a greater photostability and higher signal intensity under identical illumination conditions compared to existing fluorescence protein variants. Here, StayGold protein fusions were used to generate virus-like particles (StayGold-VLPs) to achieve hour-long 3D single-virus tracking (SVT) with 1000 localizations per second (kHz sampling rate) in live cells. The expanded photon budget from StayGold protein fusions prolonged the tracking duration, facilitating a comprehensive study of viral trafficking dynamics with high temporal resolution over long time scales. The development of StayGold-VLPs presents a simple and general VLP labeling strategy for better performance in SVT, enabling exponentially more information to be collected from single trajectories and allowing for the future possibility of observing the entire life cycle of a single virus.
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Affiliation(s)
- Yuxin Lin
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Jack Exell
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Haoting Lin
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Chen Zhang
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Kevin D Welsher
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
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2
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Lin Y, Exell J, Lin H, Zhang C, Welsher KD. Hour-long, Kilohertz Sampling Rate 3D Single-virus Tracking in Live Cells Enabled by StayGold Fluorescent Protein Fusions. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.14.585070. [PMID: 38559049 PMCID: PMC10979972 DOI: 10.1101/2024.03.14.585070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
The viral infection process covers a large range of spatiotemporal scales. Tracking the viral infection process with fluorescent labels over long durations while maintaining a fast sampling rate requires bright and highly photostable labels. StayGold is a recently identified green fluorescent protein that has a greater photostability and higher signal intensity under identical illumination conditions as compared to existing fluorescence protein variants. Here, StayGold protein fusions were used to generate virus-like particles (StayGold-VLPs) to achieve hour-long 3D single-virus tracking (SVT) with one thousand localizations per second (kHz sampling rate) in live cells. The expanded photon budget from StayGold protein fusions prolonged the tracking duration, facilitating a comprehensive study of viral trafficking dynamics with high temporal resolution over long timescales. The development of StayGold-VLPs presents a simple and general VLP labeling strategy for better performance in SVT, enabling exponentially more information to be collected from single trajectories and allowing for the future possibility of observing the whole life cycle of a single virus.
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Affiliation(s)
- Yuxin Lin
- Department of Chemistry, Duke University; Durham, North Carolina 27708, United States
| | - Jack Exell
- Department of Chemistry, Duke University; Durham, North Carolina 27708, United States
| | - Haoting Lin
- Department of Chemistry, Duke University; Durham, North Carolina 27708, United States
| | - Chen Zhang
- Department of Chemistry, Duke University; Durham, North Carolina 27708, United States
| | - Kevin D. Welsher
- Department of Chemistry, Duke University; Durham, North Carolina 27708, United States
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3
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Chaudhury A, Swarnakar S, Pattnaik GP, Varshney GK, Chakraborty H, Basu JK. Peptide-Induced Fusion of Dynamic Membrane Nanodomains: Implications in a Viral Entry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:17713-17722. [PMID: 38031897 DOI: 10.1021/acs.langmuir.3c02230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2023]
Abstract
Enveloped viruses infect host cells via protein-mediated membrane fusion. However, insights into the microscopic rearrangement induced by the viral proteins and peptides have not yet emerged. Here, we report a new methodology to extract viral fusion peptide (FP)-mediated biomembrane dynamical nanodomain fusion parameter, λ, based on stimulated emission depletion microscopy coupled with fluorescence correlation spectroscopy. We also define another dynamical parameter membrane gradient, defined in terms of the ratio of average lipid diffusion coefficients across dynamic crossover length scales, ξ. Significantly, we observe that λ as well as these mobility gradients are larger in the stiffer liquid-ordered (Lo) phase compared to the liquid-disordered phase and are more effective at the smaller nanodomain interfaces, which are only present in the Lo phase. The results could possibly help to resolve a long-standing puzzle about the enhanced fusogenicity of FP in the Lo phase. Results obtained from the diffusion results have been correlated with the human immunodeficiency virus gp41 FP-induced membrane fusion.
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Affiliation(s)
- Anurag Chaudhury
- Department of Physics, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Shovon Swarnakar
- Department of Physics, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | | | - Gopal K Varshney
- Department of Physics, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Hirak Chakraborty
- School of Chemistry, Sambalpur University, Jyoti Vihar, Burla, Odisha 768019, India
| | - Jaydeep Kumar Basu
- Department of Physics, Indian Institute of Science, Bengaluru, Karnataka 560012, India
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4
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Sengar A, Cervantes M, Bondalapati ST, Hess T, Kasson PM. Single-Virus Fusion Measurements Reveal Multiple Mechanistically Equivalent Pathways for SARS-CoV-2 Entry. J Virol 2023; 97:e0199222. [PMID: 37133381 DOI: 10.1128/jvi.01992-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/04/2023] Open
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds to cell surface receptors and is activated for membrane fusion and cell entry via proteolytic cleavage. Phenomenological data have shown that SARS-CoV-2 can be activated for entry at either the cell surface or in endosomes, but the relative roles in different cell types and mechanisms of entry have been debated. Here, we used single-virus fusion experiments and exogenously controlled proteases to probe activation directly. We found that plasma membrane and an appropriate protease are sufficient to support SARS-CoV-2 pseudovirus fusion. Furthermore, fusion kinetics of SARS-CoV-2 pseudoviruses are indistinguishable no matter which of a broad range of proteases is used to activate the virus. This suggests that the fusion mechanism is insensitive to protease identity or even whether activation occurs before or after receptor binding. These data support a model for opportunistic fusion by SARS-CoV-2 in which the subcellular location of entry likely depends on the differential activity of airway, cellsurface, and endosomal proteases, but all support infection. Inhibition of any single host protease may thus reduce infection in some cells but may be less clinically robust. IMPORTANCE SARS-CoV-2 can use multiple pathways to infect cells, as demonstrated recently when new viral variants switched dominant infection pathways. Here, we used single-virus fusion experiments together with biochemical reconstitution to show that these multiple pathways coexist simultaneously and specifically that the virus can be activated by different proteases in different cellular compartments with mechanistically identical effects. The consequences of this are that the virus is evolutionarily plastic and that therapies targeting viral entry should address multiple pathways at once to achieve optimal clinical effects.
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Affiliation(s)
- Anjali Sengar
- Department of Molecular Physiology, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
| | - Marcos Cervantes
- Department of Molecular Physiology, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
| | - Sai T Bondalapati
- Department of Molecular Physiology, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
| | - Tobin Hess
- Department of Molecular Physiology, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
| | - Peter M Kasson
- Department of Molecular Physiology, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, Global Infectious Diseases Institute, University of Virginia, Charlottesville, Virginia, USA
- Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
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5
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Mannsverk S, Villamil Giraldo AM, Kasson PM. Influenza Virus Membrane Fusion Is Promoted by the Endosome-Resident Phospholipid Bis(monoacylglycero)phosphate. J Phys Chem B 2022; 126:10445-10451. [PMID: 36468619 PMCID: PMC9761668 DOI: 10.1021/acs.jpcb.2c06642] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The phospholipid bis(monoacylglycero)phosphate (BMP) is enriched in late endosomal and endolysosomal membranes and is believed to be involved in membrane deformation and generation of intralumenal vesicles within late endosomes. Previous studies have demonstrated that BMP promotes membrane fusion of several enveloped viruses, but a limited effect has been found on influenza virus. Here, we report the use of single-virus fusion assays to dissect BMP's effect on influenza virus fusion in greater depth. In agreement with prior reports, we found that hemifusion kinetics and efficiency were unaffected by the addition of 10-20 mol % BMP to the target membrane. However, using an assay for fusion pore formation and genome exposure, we found full fusion efficiency to be substantially enhanced by the addition of 10-20 mol % BMP to the target membrane, while the kinetics remained unaffected. By comparing BMP to other negatively charged phospholipids, we found the effect on fusion efficiency mainly attributable to headgroup charge, although we also hypothesize a role for BMP's unusual chemical structure. Our results suggest that BMP function as a permissive factor for a wider range of viruses than previously reported. We hypothesize that BMP may be a general cofactor for endosomal entry of enveloped viruses.
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Affiliation(s)
- Steinar Mannsverk
- Science
for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala 75124, Sweden
| | - Ana M. Villamil Giraldo
- Science
for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala 75124, Sweden
| | - Peter M. Kasson
- Science
for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala 75124, Sweden,Departments
of Molecular Physiology and Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908, United States,
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6
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Xu C, Ren XH, Han D, Peng Y, Lei JJ, Yu LX, Liu LJ, Xu WC, Cheng SX. Precise Detection on Cell-Cell Fusion by a Facile Molecular Beacon-Based Method. Anal Chem 2022; 94:17334-17340. [PMID: 36456915 DOI: 10.1021/acs.analchem.2c04852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Cell-cell fusion studies provide an experimental platform for evaluating disease progression and investigating cell infection. However, to realize sensitive and quantitative detection on cell-cell fusion is still a challenge. Herein, we report a facile molecular beacon (MB)-based method for precise detection on cell-cell fusion. By transfection of the spike protein (S protein) and enhanced green fluorescent protein (EGFP) in HEK 293 cells, the virus-mimicking fusogenic effector cells 293-S-EGFP cells were constructed to interact with target cells. Before mixing the effector cells with the target cells, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression in 293-S-EGFP cells was silenced, and the MB for GAPDH mRNA detection was delivered into the GAPDH silenced 293-S-EGFP cells. Once cell-cell fusion occurred, MB migrated from the GAPDH silenced effector cells to the target cells and hybridized with GAPDH mRNA in the target cells to induce fluorescence emission. The cell-cell fusion can be easily visualized and quantitated by fluorescence microscopy and flow cytometry. The fluorescence intensity is strongly dependent on the number of fused target cells. This MB-based method can easily identify the differences in the cell fusions for various target cells with different angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) expression levels, resulting in dramatically different fluorescence intensities in fused target cells. Our study provides a convenient and efficient quantitative detection approach to study cell-cell fusion.
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Affiliation(s)
- Chang Xu
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Xiao-He Ren
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Di Han
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Yan Peng
- Department of Pharmacy, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Jin-Ju Lei
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Luo-Xiao Yu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Ling-Juan Liu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Wei-Chao Xu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Si-Xue Cheng
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
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7
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Villamil Giraldo AM, Mannsverk S, Kasson PM. Measuring single-virus fusion kinetics using an assay for nucleic acid exposure. Biophys J 2022; 121:4467-4475. [PMID: 36330566 PMCID: PMC9748363 DOI: 10.1016/j.bpj.2022.11.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/26/2022] [Accepted: 10/31/2022] [Indexed: 11/11/2022] Open
Abstract
The kinetics by which individual enveloped viruses fuse with membranes provide an important window into viral-entry mechanisms. We have developed a real-time assay using fluorescent probes for single-virus genome exposure than can report on stages of viral entry including or subsequent to fusion pore formation and prior to viral genome trafficking. We accomplish this using oxazole yellow nucleic-acid-binding dyes, which can be encapsulated in the lumen of target membranes to permit specific detection of fusion events. Since increased fluorescence of the dye occurs only when it encounters viral genome via a fusion pore and binds, this assay excludes content leakage without fusion. Using this assay, we show that influenza virus fuses with liposomes of different sizes with indistinguishable kinetics by both testing liposomes extruded through pores of different radii and showing that the fusion kinetics of individual liposomes are uncorrelated with the size of the liposome. These results suggest that the starting curvature of such liposomes does not control the rate-limiting steps in influenza entry.
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Affiliation(s)
- Ana M Villamil Giraldo
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Steinar Mannsverk
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Peter M Kasson
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden; Departments of Molecular Physiology and Biomedical Engineering, University of Virginia, Charlottesville, Virginia.
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8
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Haldar S. Recent Developments in Single-Virus Fusion Assay. J Membr Biol 2022; 255:747-755. [PMID: 36173449 DOI: 10.1007/s00232-022-00270-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Accepted: 09/13/2022] [Indexed: 12/24/2022]
Abstract
Viral infection is a global health hazard. A crucial step in the infection cycle of enveloped viruses is the fusion of viral and host cellular membranes, which permits the transfer of the viral genome to the host cells. Membrane fusion is a ubiquitous process involved in sperm-egg fusion, exocytosis, vesicular trafficking, and viral entry to host cells. While different protein machineries catalyze the diverse fusion processes, the essential step, i.e., merging of two lipid bilayers against a kinetic energy barrier, is the same. Therefore, viral fusion machineries/pathways are not only the sites for antiviral drug development but also serve as model fusogens. Ensemble-based spectroscopic approaches or bulk fusion assays have yielded valuable insights regarding the fusion processes. However, due to the stochastic nature of the fusion events, ensemble-based assays do not permit synchronization of all the fusion events, and the molecular steps leading to fusion pore opening cannot be resolved entirely and correlated with the structural changes in viral fusion proteins. Several single-virus fusion assays have been developed to circumvent these issues. The review describes the recent advancements in single-virus/particle fusion assays using the Influenza virus as a paradigm.
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Affiliation(s)
- Sourav Haldar
- Division of Virus Research and Therapeutics, CSIR-Central Drug Research Institute, Lucknow, Uttar Pradesh, 226031, India. .,Academy of Scientific and Innovative Research, Ghaziabad, Uttar Pradesh, India.
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9
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Mechanistic dissection of antibody inhibition of influenza entry yields unexpected heterogeneity. Biophys J 2022:S0006-3495(22)00864-5. [DOI: 10.1016/j.bpj.2022.10.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 10/10/2022] [Accepted: 10/17/2022] [Indexed: 11/21/2022] Open
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10
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Lam A, Yuan DS, Ahmed SH, Rawle RJ. Viral Size Modulates Sendai Virus Binding to Cholesterol-Stabilized Receptor Nanoclusters. J Phys Chem B 2022; 126:6802-6810. [PMID: 36001793 PMCID: PMC9484459 DOI: 10.1021/acs.jpcb.2c03830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 08/12/2022] [Indexed: 11/29/2022]
Abstract
Binding to the host membrane is the initial infection step for animal viruses. Sendai virus (SeV), the model respirovirus studied here, utilizes sialic-acid-conjugated glycoproteins and glycolipids as receptors for binding. In a previous report studying single virus binding to supported lipid bilayers (SLBs), we found a puzzling mechanistic difference between the binding of SeV and influenza A virus (strain X31, IAVX31). Both viruses use similar receptors and exhibit similar cooperative binding behavior, but whereas IAVX31 binding was altered by SLB cholesterol concentration, which can stabilize receptor nanoclusters, SeV was not. Here, we propose that differences in viral size distributions can explain this discrepancy; viral size could alter the number of virus-receptor interactions in the contact area and, therefore, the sensitivity to receptor nanoclusters. To test this, we compared the dependence of SeV binding on SLB cholesterol concentration between size-filtered and unfiltered SeV. At high receptor density, the unfiltered virus showed little dependence, but the size-filtered virus exhibited a linear cholesterol dependence, similar to IAVX31. However, at low receptor densities, the unfiltered virus did exhibit a cholesterol dependence, indicating that receptor nanoclusters enhance viral binding only when the number of potential virus-receptor interactions is small enough. We also studied the influence of viral size and receptor nanoclusters on viral mobility following binding. Whereas differences in viral size greatly influenced mobility, the effect of receptor nanoclusters on mobility was small. Together, our results highlight the mechanistic salience of both the distribution of viral sizes and the lateral distribution of receptors in a viral infection.
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Affiliation(s)
- Amy Lam
- Department of Chemistry, Williams
College, Williamstown, Massachusetts01267, United States
| | - Daniel S. Yuan
- Department of Chemistry, Williams
College, Williamstown, Massachusetts01267, United States
| | - Samir H. Ahmed
- Department of Chemistry, Williams
College, Williamstown, Massachusetts01267, United States
| | - Robert J. Rawle
- Department of Chemistry, Williams
College, Williamstown, Massachusetts01267, United States
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11
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Lam A, Kirkland OO, Anderson PF, Seetharaman N, Vujovic D, Thibault PA, Azarm KD, Lee B, Rawle RJ. Single-virus assay reveals membrane determinants and mechanistic features of Sendai virus binding. Biophys J 2022; 121:956-965. [PMID: 35150620 PMCID: PMC8943810 DOI: 10.1016/j.bpj.2022.02.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Revised: 01/11/2022] [Accepted: 02/07/2022] [Indexed: 11/17/2022] Open
Abstract
Sendai virus (SeV, formally murine respirovirus) is a membrane-enveloped, negative-sense RNA virus in the Paramyxoviridae family and is closely related to human parainfluenza viruses. SeV has long been utilized as a model paramyxovirus and has recently gained attention as a viral vector candidate for both laboratory and clinical applications. To infect host cells, SeV must first bind to sialic acid glycolipid or glycoprotein receptors on the host cell surface via its hemagglutinin-neuraminidase (HN) protein. Receptor binding induces a conformational change in HN, which allosterically triggers the viral fusion (F) protein to catalyze membrane fusion. While it is known that SeV binds to α2,3-linked sialic acid receptors, and there has been some study into the chemical requirements of those receptors, key mechanistic features of SeV binding remain unknown, in part because traditional approaches often convolve binding and fusion. Here, we develop and employ a fluorescence microscopy-based assay to observe SeV binding to supported lipid bilayers (SLBs) at the single-particle level, which easily disentangles binding from fusion. Using this assay, we investigate mechanistic questions of SeV binding. We identify chemical structural features of ganglioside receptors that influence viral binding and demonstrate that binding is cooperative with respect to receptor density. We measure the characteristic decay time of unbinding and provide evidence supporting a "rolling" mechanism of viral mobility following receptor binding. We also study the dependence of binding on target cholesterol concentration. Interestingly, we find that although SeV binding shows striking parallels in cooperative binding with a prior report of Influenza A virus, it does not demonstrate a similar sensitivity to cholesterol concentration and receptor nanocluster formation.
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Affiliation(s)
- Amy Lam
- Department of Chemistry, Williams College, Williamstown, Massachusetts
| | | | | | | | - Dragan Vujovic
- Department of Chemistry, Williams College, Williamstown, Massachusetts
| | - Patricia A Thibault
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Kristopher D Azarm
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Benhur Lee
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Robert J Rawle
- Department of Chemistry, Williams College, Williamstown, Massachusetts.
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12
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Liu KN, Boxer SG. Single-virus content-mixing assay reveals cholesterol-enhanced influenza membrane fusion efficiency. Biophys J 2021; 120:4832-4841. [PMID: 34536389 DOI: 10.1016/j.bpj.2021.09.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 08/05/2021] [Accepted: 09/09/2021] [Indexed: 10/20/2022] Open
Abstract
To infect a cell, enveloped viruses must first undergo membrane fusion, which proceeds through a hemifusion intermediate, followed by the formation of a fusion pore through which the viral genome is transferred to a target cell. Single-virus fusion studies to elucidate the dynamics of content mixing typically require extensive fluorescent labeling of viral contents. The labeling process must be optimized depending on the virus identity and strain and can potentially be perturbative to viral fusion behavior. Here, we introduce a single-virus assay in which content-labeled vesicles are bound to unlabeled influenza A virus (IAV) to eliminate the problematic step of content-labeling virions. We use fluorescence microscopy to observe individual, pH-triggered content mixing and content-loss events between IAV and target vesicles of varying cholesterol compositions. We show that target membrane cholesterol increases the efficiency of IAV content mixing and decreases the fraction of content-mixing events that result in content loss. These results are consistent with previous findings that cholesterol stabilizes pore formation in IAV entry and limits leakage after pore formation. We also show that content loss due to hemagglutinin fusion peptide engagement with the target membrane is independent of composition. This approach is a promising strategy for studying the single-virus content-mixing kinetics of other enveloped viruses.
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Affiliation(s)
- Katherine N Liu
- Department of Chemistry, Stanford University, Stanford, California
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, California.
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13
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Membrane dynamics are slowed for Alexa594-labeled membrane proteins due to substrate interactions. BBA ADVANCES 2021; 1:100026. [PMID: 37082018 PMCID: PMC10074974 DOI: 10.1016/j.bbadva.2021.100026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The addition of fluorescent dyes to proteins, lipids and other biological molecules can affect a range of processes such as mobility, molecular interactions, localization, and, ultimately, function. The dynamics of a protein can be dramatically affected if the label interacts non-specifically with the substrate or with other molecules in the system. To test how dye-substrate interactions affect protein diffusion, fluorescence recovery after photobleaching (FRAP) measurements were designed to explicitly determine the role of the dye on the diffusion of a transmembrane protein, Syntaxin1a, expressed on the cell surface. Syntaxin1a, was tagged with EGFP on the extracellular side and an EGFP nanobody with or without a dye label was attached. FRAP was performed on Syx1a-EGFP and the choice of cell growth substrate affected mobility in the presence of a dye labeled nanobody. This work provides evidence for choosing fibronectin (Fn) over poly-L-lysine (PLL) in FRAP and single molecule tracking measurements when using Alexa594, a common probe for red fluorescent measurements. Alexa594-labeled nanobody but not unlabeled nanobody, dramatically reduced the mobility of Syx1a-EGFP when cells were cultured on PLL. However, when Fn was used, the mobility returned. Mobility measured by single molecule tracking measurements align with the FRAP measurements with Fn coated surfaces being more mobile than PLL.
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14
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Park A, Graceffa O, Rawle RJ. Kinetic Modeling of West Nile Virus Fusion Indicates an Off-Pathway State. ACS Infect Dis 2020; 6:3260-3268. [PMID: 33201665 DOI: 10.1021/acsinfecdis.0c00637] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
West Nile virus (WNV) is a prominent mosquito-borne flavivirus that causes febrile illness in humans. To infect host cells, WNV virions first bind to plasma membrane receptors, then initiate membrane fusion following endocytosis. The viral transmembrane E protein, triggered by endosomal pH, catalyzes fusion while undergoing a dimer-to-trimer transition. Previously, single-particle WNV fusion data was interrogated with a stochastic cellular automaton simulation, which modeled the E proteins during the fusion process. The results supported a linear fusion mechanism, with E protein trimerization being rate-limiting. Here, we present corrections to the previous simulation, and apply them to the WNV fusion data. We observe that a linear mechanism is no longer sufficient to fit the data. Instead, an off-pathway state is necessary; these results are corroborated by per virus chemical kinetics modeling. When compared with a similar Zika virus fusion model, this suggests that off-pathway fusion mechanisms may characterize flaviviruses more broadly.
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Affiliation(s)
- Abraham Park
- Department of Chemistry, Williams College, Williamstown, Massachusetts 01267, United States
| | - Olivia Graceffa
- Department of Chemistry, Williams College, Williamstown, Massachusetts 01267, United States
| | - Robert J. Rawle
- Department of Chemistry, Williams College, Williamstown, Massachusetts 01267, United States
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15
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Haldar S, Okamoto K, Dunning RA, Kasson PM. Precise Triggering and Chemical Control of Single-Virus Fusion within Endosomes. J Virol 2020; 95:e01982-20. [PMID: 33115879 PMCID: PMC7737740 DOI: 10.1128/jvi.01982-20] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 10/07/2020] [Indexed: 11/20/2022] Open
Abstract
Many enveloped viruses infect cells within endocytic compartments. The pH drop that accompanies endosomal maturation, often in conjunction with proteolysis, triggers viral proteins to insert into the endosomal membrane and drive fusion. Fusion dynamics have been studied by tracking viruses within living cells, which limits the precision with which fusion can be synchronized and controlled, and reconstituting viral fusion to synthetic membranes, which introduces nonphysiological membrane curvature and composition. To overcome these limitations, we report chemically controllable triggering of single-virus fusion within endosomes. We isolated influenza (A/Aichi/68; H3N2) virus:endosome conjugates from cells, immobilized them in a microfluidic flow cell, and rapidly and controllably triggered fusion. Observed lipid-mixing kinetics were surprisingly similar to those of influenza virus fusion with model membranes of opposite curvature: 80% of single-virus events had indistinguishable kinetics. This result suggests that endosomal membrane curvature is not a key permissive feature for viral entry, at least lipid mixing. The assay preserved endosomal membrane asymmetry and protein composition, providing a platform to test how cellular restriction factors and altered endosomal trafficking affect viral membrane fusion.IMPORTANCE Many enveloped viruses infect cells via fusion to endosomes, but controlling this process within living cells has been challenging. We studied the fusion of influenza virus virions to endosomes in a chemically controllable manner. Extracting virus:endosome conjugates from cells and exogenously triggering fusion permits precise study of virus:endosome fusion kinetics. Surprisingly, endosomal curvature does not grossly alter fusion kinetics, although membrane deformability does. This supports a model for influenza virus entry where cells restrict or permit membrane fusion by changing deformability, for instance, using interferon-induced proteins.
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Affiliation(s)
- Sourav Haldar
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Kenta Okamoto
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Rebecca A Dunning
- Department of Molecular Physiology, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia, USA
| | - Peter M Kasson
- Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
- Department of Molecular Physiology, University of Virginia, Charlottesville, Virginia, USA
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia, USA
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Ward AE, Kiessling V, Pornillos O, White JM, Ganser-Pornillos BK, Tamm LK. HIV-cell membrane fusion intermediates are restricted by Serincs as revealed by cryo-electron and TIRF microscopy. J Biol Chem 2020; 295:15183-15195. [PMID: 32788212 PMCID: PMC7650252 DOI: 10.1074/jbc.ra120.014466] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 07/19/2020] [Indexed: 12/13/2022] Open
Abstract
To enter a cell and establish infection, HIV must first fuse its lipid envelope with the host cell plasma membrane. Whereas the process of HIV membrane fusion can be tracked by fluorescence microscopy, the 3D configuration of proteins and lipids at intermediate steps can only be resolved with cryo-electron tomography (cryoET). However, cryoET of whole cells is technically difficult. To overcome this problem, we have adapted giant plasma membrane vesicles (or blebs) from native cell membranes expressing appropriate receptors as targets for fusion with HIV envelope glycoprotein-expressing pseudovirus particles with and without Serinc host restriction factors. The fusion behavior of these particles was probed by TIRF microscopy on bleb-derived supported membranes. Timed snapshots of fusion of the same particles with blebs were examined by cryo-ET. The combination of these methods allowed us to characterize the structures of various intermediates on the fusion pathway and showed that when Serinc3 or Serinc5 (but not Serinc2) were present, later fusion products were more prevalent, suggesting that Serinc3/5 act at multiple steps to prevent progression to full fusion. In addition, the antifungal amphotericin B reversed Serinc restriction, presumably by intercalation into the fusing membranes. Our results provide a highly detailed view of Serinc restriction of HIV-cell membrane fusion and thus extend current structural and functional information on Serinc as a lipid-binding protein.
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Affiliation(s)
- Amanda E Ward
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Owen Pornillos
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Judith M White
- Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Barbie K Ganser-Pornillos
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA.
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA; Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, Virginia, USA.
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Target Membrane Cholesterol Modulates Single Influenza Virus Membrane Fusion Efficiency but Not Rate. Biophys J 2020; 118:2426-2433. [PMID: 32298636 DOI: 10.1016/j.bpj.2020.03.021] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 03/09/2020] [Accepted: 03/23/2020] [Indexed: 12/11/2022] Open
Abstract
Host lipid composition influences many stages of the influenza A virus (IAV) entry process, including initial binding of IAV to sialylated glycans, fusion between the viral envelope and the host membrane, and the formation of a fusion pore through which the viral genome is transferred into a target cell. In particular, target membrane cholesterol has been shown to preferentially associate with virus receptors and alter physical properties of the membrane like fluidity and curvature. These properties affect both IAV binding and fusion, which makes it difficult to isolate the role of cholesterol in IAV fusion from receptor binding effects. Here, we develop a fusion assay that uses synthetic DNA-lipid conjugates as surrogate viral receptors to tether virions to target vesicles. To avoid the possibly perturbative effect of adding a self-quenched concentration of dye-labeled lipids to the viral membrane, we tether virions to lipid-labeled target vesicles and use fluorescence microscopy to detect individual, pH-triggered IAV membrane fusion events. Through this approach, we find that cholesterol in the target membrane enhances the efficiency of single-particle IAV lipid mixing, whereas the rate of lipid mixing is independent of cholesterol composition. We also find that the single-particle kinetics of influenza lipid mixing to target membranes with different cholesterol compositions is independent of receptor binding, suggesting that cholesterol-mediated spatial clustering of viral receptors within the target membrane does not significantly affect IAV hemifusion. These results are consistent with the hypothesis that target membrane cholesterol increases lipid mixing efficiency by altering host membrane curvature.
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