scholarly journals Dynamics of SARS-CoV-2 Spike Proteins in Cell Entry: Control Elements in the Amino-Terminal Domains

mBio ◽  
2021 ◽  
Author(s):  
Enya Qing ◽  
Tom Kicmal ◽  
Binod Kumar ◽  
Grant M. Hawkins ◽  
Emily Timm ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Membrane Fusion ◽  
Cell Entry ◽  
Adaptive Changes ◽  
Amino Terminal ◽  
Spike Proteins ◽  
Terminal Domains

Adaptive changes that increase SARS-CoV-2 transmissibility may expand and prolong the coronavirus disease 2019 (COVID-19) pandemic. Transmission requires metastable and dynamic spike proteins that bind viruses to cells and catalyze virus-cell membrane fusion.

scholarly journals Characterization of the Early Events in Dengue Virus Cell Entry by Biochemical Assays and Single-Virus Tracking

2007 ◽  
Vol 81 (21) ◽  
pp. 12019-12028 ◽  
Author(s):  
Hilde M. van der Schaar ◽  
Michael J. Rust ◽  
Barry-Lee Waarts ◽  
Heidi van der Ende-Metselaar ◽  
Richard J. Kuhn ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Dengue Virus ◽  
Membrane Fusion ◽  
High Ratio ◽  
Cell Entry ◽  
Viral Membrane ◽  
Virus Particles ◽  
Biochemical Assays ◽  
Particle Ratio ◽  
Infectious Unit

ABSTRACT In this study, we investigated the cell entry characteristics of dengue virus (DENV) type 2 strain S1 on mosquito, BHK-15, and BS-C-1 cells. The concentration of virus particles measured by biochemical assays was found to be substantially higher than the number of infectious particles determined by infectivity assays, leading to an infectious unit-to-particle ratio of approximately 1:2,600 to 1:72,000, depending on the specific assays used. In order to explain this high ratio, we investigated the receptor binding and membrane fusion characteristics of single DENV particles in living cells using real-time fluorescence microscopy. For this purpose, DENV was labeled with the lipophilic fluorescent probe DiD (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine, 4-chlorobenzenesulfonate salt). The surface density of the DiD dye in the viral membrane was sufficiently high to largely quench the fluorescence intensity but still allowed clear detection of single virus particles. Fusion of the viral membrane with the cell membrane was evident as fluorescence dequenching. It was observed that DENV binds very inefficiently to the cells used, explaining at least in part the high infectious unit-to-particle ratio. The particles that did bind to the cells showed different types of transport behavior leading to membrane fusion in both the periphery and perinuclear regions of the cell. Membrane fusion was observed in 1 out of 6 bound virus particles, indicating that a substantial fraction of the virus has the capacity to fuse. DiD dequenching was completely inhibited by ammonium chloride, demonstrating that fusion occurs exclusively from within acidic endosomes.

scholarly journals Distinct Roles for Sialoside and Protein Receptors in Coronavirus Infection

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Enya Qing ◽  
Michael Hantak ◽  
Stanley Perlman ◽  
Tom Gallagher
Keyword(s):  
Cell Membrane ◽  
Membrane Fusion ◽  
Receptor Binding ◽  
Sialic Acids ◽  
Zoonotic Transmission ◽  
Virus Spread ◽  
Binding Domains ◽  
Protein Receptors ◽  
Cell Cell ◽  
Spike Proteins

ABSTRACT Coronaviruses (CoVs) are common human and animal pathogens that can transmit zoonotically and cause severe respiratory disease syndromes. CoV infection requires spike proteins, which bind viruses to host cell receptors and catalyze virus-cell membrane fusion. Several CoV strains have spike proteins with two receptor-binding domains, an S1A that engages host sialic acids and an S1B that recognizes host transmembrane proteins. As this bivalent binding may enable broad zoonotic CoV infection, we aimed to identify roles for each receptor in distinct infection stages. Focusing on two betacoronaviruses, murine JHM-CoV and human Middle East respiratory syndrome coronavirus (MERS-CoV), we found that virus particle binding to cells was mediated by sialic acids; however, the transmembrane protein receptors were required for a subsequent virus infection. These results favored a two-step process in which viruses first adhere to sialic acids and then require subsequent engagement with protein receptors during infectious cell entry. However, sialic acids sufficiently facilitated the later stages of virus spread through cell-cell membrane fusion, without requiring protein receptors. This virus spread in the absence of the prototype protein receptors was increased by adaptive S1A mutations. Overall, these findings reveal roles for sialic acids in virus-cell binding, viral spike protein-directed cell-cell fusion, and resultant spread of CoV infections. IMPORTANCE CoVs can transmit from animals to humans to cause serious disease. This zoonotic transmission uses spike proteins, which bind CoVs to cells with two receptor-binding domains. Here, we identified the roles for the two binding processes in the CoV infection process. Binding to sialic acids promoted infection and also supported the intercellular expansion of CoV infections through syncytial development. Adaptive mutations in the sialic acid-binding spike domains increased the intercellular expansion process. These findings raise the possibility that the lectin-like properties of many CoVs contribute to facile zoonotic transmission and intercellular spread within infected organisms.

scholarly journals Coronavirus and Influenza Virus Proteolytic Priming Takes Place in Tetraspanin-Enriched Membrane Microdomains

2015 ◽  
Vol 89 (11) ◽  
pp. 6093-6104 ◽  
Author(s):  
James T. Earnest ◽  
Michael P. Hantak ◽  
Jung-Eun Park ◽  
Tom Gallagher
Keyword(s):  
Cell Membrane ◽  
Membrane Fusion ◽  
Target Cell ◽  
Influenza A ◽  
Virus Entry ◽  
Cell Entry ◽  
Membrane Microdomains ◽  
Enveloped Viruses ◽  
Viral Surface ◽  
Surface Glycoproteins

ABSTRACTCoronaviruses (CoVs) and low-pathogenicity influenza A viruses (LP IAVs) depend on target cell proteases to cleave their viral glycoproteins and prime them for virus-cell membrane fusion. Several proteases cluster into tetraspanin-enriched microdomains (TEMs), suggesting that TEMs are preferred virus entry portals. Here we found that several CoV receptors and virus-priming proteases were indeed present in TEMs. Isolated TEMs, when mixed with CoV and LP IAV pseudoparticles, cleaved viral fusion proteins to fusion-primed fragments and potentiated viral transductions. That entering viruses utilize TEMs as a protease source was further confirmed using tetraspanin antibodies and tetraspanin short hairpin RNAs (shRNAs). Tetraspanin antibodies inhibited CoV and LP IAV infections, but their virus-blocking activities were overcome by expressing excess TEM-associated proteases. Similarly, cells with reduced levels of the tetraspanin CD9 resisted CoV pseudoparticle transductions but were made susceptible by overproducing TEM-associated proteases. These findings indicated that antibodies and CD9 depletions interfere with viral proteolytic priming in ways that are overcome by surplus proteases. TEMs appear to be exploited by some CoVs and LP IAVs for appropriate coengagement with cell receptors and proteases.IMPORTANCEEnveloped viruses use their surface glycoproteins to catalyze membrane fusion, an essential cell entry step. Host cell components prime these viral surface glycoproteins to catalyze membrane fusion at specific times and places during virus cell entry. Among these priming components are proteases, which cleave viral surface glycoproteins, unleashing them to refold in ways that catalyze virus-cell membrane fusions. For some enveloped viruses, these proteases are known to reside on target cell surfaces. This research focuses on coronavirus and influenza A virus cell entry and identifies TEMs as sites of viral proteolysis, thereby defining subcellular locations of virus priming with greater precision. Implications of these findings extend to the use of virus entry antagonists, such as protease inhibitors, which might be most effective when localized to these microdomains.

Trophoblast Cell Membrane Interactions at Implantation

1970 ◽  
Vol 28 ◽  
pp. 310-311
Author(s):  
A. C. Enders
Keyword(s):  
Epithelial Cells ◽  
Cell Membrane ◽  
Membrane Fusion ◽  
Trophoblast Cell ◽  
Membrane Interactions ◽  
Uterine Epithelial Cells ◽  
Functional Complex ◽  
Cytotrophoblast Cells ◽  
Complex Relationships ◽  
Syncytial Trophoblast

The alteration in membrane relationships seen at implantation include 1) interaction between cytotrophoblast cells to form syncytial trophoblast and addition to the syncytium by subsequent fusion of cytotrophoblast cells, 2) formation of a wide variety of functional complex relationships by trophoblast with uterine epithelial cells in the process of invasion of the endometrium, and 3) in the case of the rabbit, fusion of some uterine epithelial cells with the trophoblast.Formation of syncytium is apparently a membrane fusion phenomenon in which rapid confluence of cytoplasm often results in isolation of residual membrane within masses of syncytial trophoblast. Often the last areas of membrane to disappear are those including a desmosome where the cell membranes are apparently held apart from fusion.

scholarly journals Molecular diversity in amino-terminal domains of human calpastatin by exon skipping.

1992 ◽  
Vol 267 (12) ◽  
pp. 8437-8442
Author(s):  
W.J. Lee ◽  
H Ma ◽  
E Takano ◽  
H.Q. Yang ◽  
M Hatanaka ◽  
...  
Keyword(s):  
Molecular Diversity ◽  
Exon Skipping ◽  
Amino Terminal ◽  
Terminal Domains

Long‐Residence Pneumonia Vaccine Developed Using PEG‐Grafted Hybrid Nanovesicles from Cell Membrane Fusion of Mycoplasma and IFN‐γ‐Primed Macrophages

Small ◽  
2021 ◽  
pp. 2101183
Author(s):  
Zhenzhen Zhang ◽  
Haiyan Wang ◽  
Xing Xie ◽  
Rong Chen ◽  
Jun Li ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Membrane Fusion ◽  
Ifn Γ

Insights into a Structure-Based Mechanism of Viral Membrane Fusion

2000 ◽  
Vol 20 (6) ◽  
pp. 557-570 ◽  
Author(s):  
Danika L. LeDuc ◽  
Yeon-Kyun Shin
Keyword(s):  
Membrane Fusion ◽  
General Structure ◽  
Viral Membrane ◽  
Induced Membrane ◽  
Alternative Scenario ◽  
Influenza Hemagglutinin ◽  
Hiv Gp120 ◽  
Viral Membrane Fusion ◽  
Spike Proteins

A number of different viral spike proteins, responsible for membrane fusion, show striking similarities in their core structures. The prospect of developing a general structure-based mechanism seems plausible in light of these newly determined structures. Influenza hemagglutinin (HA) is the best-studied fusion machine, whose action has previously been described by a hypothetical “spring-loaded” model. This model has recently been extended to explain the mechanism of other systems, such as HIV gp120–gp41. However, evidence supporting this idea is insufficient, requiring re-examination of the mechanism of HA-induced membrane fusion. Recent experiments with a shortened construct of HA, which is able to induce lipid mixing, have provided evidence for an alternative scenario for HA-induced membrane fusion and perhaps that of other viral systems.

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