scholarly journals Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

2019 ◽  
Vol 6 (1) ◽  
pp. 341-363 ◽  
Author(s):  
Roy Duncan
Keyword(s):  
Membrane Fusion ◽  
Fusion Proteins ◽  
Syncytium Formation ◽  
Nonstructural Proteins ◽  
Enveloped Virus ◽  
Fast Proteins ◽  
Nonenveloped Virus ◽  
Functional Features ◽  
Membrane Fusion Proteins ◽  
Viral Membrane Fusion

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

scholarly journals Measurement of membrane fusion activity from viral membrane fusion proteins based on a fusion-dependent promoter induction system in insect cells

2001 ◽  
Vol 82 (10) ◽  
pp. 2519-2529 ◽  
Author(s):  
J. M. Slack ◽  
G. W. Blissard
Keyword(s):  
Membrane Fusion ◽  
Cell Fusion ◽  
Insect Cells ◽  
Syncytium Formation ◽  
Fusion Activity ◽  
Viral Membrane ◽  
Fusion Domain ◽  
Membrane Fusion Proteins ◽  
Viral Membrane Fusion ◽  
Egfp Fluorescence

A number of viral membrane fusion proteins can be expressed alone on the surface of host cells, and then triggered to induce cell-to-cell fusion or syncytium formation. Although rapid and easily observed, syncytium formation is not easily quantified and differences in fusion activity are not easily distinguished or measured. To address this problem, we developed a rapid and quantitative cell-to-cell fusion system that is useful for comparative analysis and may be suitable for high throughput screening. In this system, expression of a reporter protein, enhanced green fluorescent protein (EGFP), is dependent on cell-to-cell fusion. Spodoptera frugiperda (Sf9) insect cells expressing a chimeric Lac repressor-IE1 protein were fused to Sf9 cells containing an EGFP reporter construct under the control of a responsive lac operator-containing promoter. Membrane fusion efficiency was measured from the resulting EGFP fluorescence activity. Sf9 cells expressing the Orgyia pseudotsugata multicapsid nucleopolyhedrovirus (OpMNPV) GP64 envelope fusion protein were used as a model to test this fusion assay. Subtle changes in fusion activities of GP64 proteins containing single amino acid substitutions in a putative membrane fusion domain were distinguished, and decreases in EGFP fluorescence corresponded to decreases in the hydrophobicity in the small putative membrane fusion domain.

scholarly journals Multifaceted Sequence-Dependent and -Independent Roles for Reovirus FAST Protein Cytoplasmic Tails in Fusion Pore Formation and Syncytiogenesis

2009 ◽  
Vol 83 (23) ◽  
pp. 12185-12195 ◽  
Author(s):  
Christopher Barry ◽  
Roy Duncan
Keyword(s):  
Membrane Fusion ◽  
Fusion Proteins ◽  
Pore Formation ◽  
Syncytium Formation ◽  
Fusion Pore ◽  
Protein Fusion ◽  
Sequence Dependent ◽  
Cytoplasmic Tails ◽  
Fast Proteins ◽  
Pore Expansion

ABSTRACT Fusogenic reoviruses utilize the FAST proteins, a novel family of nonstructural viral membrane fusion proteins, to induce cell-cell fusion and syncytium formation. Unlike the paradigmatic enveloped virus fusion proteins, the FAST proteins position the majority of their mass within and internal to the membrane in which they reside, resulting in extended C-terminal cytoplasmic tails (CTs). Using tail truncations, we demonstrate that the last 8 residues of the 36-residue CT of the avian reovirus p10 FAST protein and the last 20 residues of the 68-residue CT of the reptilian reovirus p14 FAST protein enhance, but are not required for, pore expansion and syncytium formation. Further truncations indicate that the membrane-distal 12 residues of the p10 and 47 residues of the p14 CTs are essential for pore formation and that a residual tail of 21 to 24 residues that includes a conserved, membrane-proximal polybasic region present in all FAST proteins is insufficient to maintain FAST protein fusion activity. Unexpectedly, a reextension of the tail-truncated, nonfusogenic p10 and p14 constructs with scrambled versions of the deleted sequences restored pore formation and syncytiogenesis, while reextensions with heterologous sequences partially restored pore formation but failed to rescue syncytiogenesis. The membrane-distal regions of the FAST protein CTs therefore exert multiple effects on the membrane fusion reaction, serving in both sequence-dependent and sequence-independent manners as positive effectors of pore formation, pore expansion, and syncytiogenesis.

scholarly journals Viral Membrane Fusion Proteins and RNA Sorting Mechanisms for the Molecular Delivery by Exosomes

Cells ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 3043
Author(s):  
Ilya Zubarev ◽  
Dmitry Vladimirtsev ◽  
Maria Vorontsova ◽  
Igor Blatov ◽  
Konstantin Shevchenko ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Targeted Delivery ◽  
Fusion Proteins ◽  
Rna Binding ◽  
Rna Binding Proteins ◽  
Viral Fusion ◽  
Viral Membrane ◽  
Membrane Fusion Proteins ◽  
Viral Membrane Fusion

The advancement of precision medicine critically depends on the robustness and specificity of the carriers used for the targeted delivery of effector molecules in the human body. Numerous nanocarriers have been explored in vivo, to ensure the precise delivery of molecular cargos via tissue-specific targeting, including the endocrine part of the pancreas, thyroid, and adrenal glands. However, even after reaching the target organ, the cargo-carrying vehicle needs to enter the cell and then escape lysosomal destruction. Most artificial nanocarriers suffer from intrinsic limitations that prevent them from completing the specific delivery of the cargo. In this respect, extracellular vesicles (EVs) seem to be the natural tool for payload delivery due to their versatility and low toxicity. However, EV-mediated delivery is not selective and is usually short-ranged. By inserting the viral membrane fusion proteins into exosomes, it is possible to increase the efficiency of membrane recognition and also ease the process of membrane fusion. This review describes the molecular details of the viral-assisted interaction between the target cell and EVs. We also discuss the question of the usability of viral fusion proteins in developing extracellular vesicle-based nanocarriers with a higher efficacy of payload delivery. Finally, this review specifically highlights the role of Gag and RNA binding proteins in RNA sorting into EVs.

scholarly journals Structural and Functional Properties of an Unusual Internal Fusion Peptide in a Nonenveloped Virus Membrane Fusion Protein

2004 ◽  
Vol 78 (6) ◽  
pp. 2808-2818 ◽  
Author(s):  
Maya Shmulevitz ◽  
Raquel F. Epand ◽  
Richard M. Epand ◽  
Roy Duncan
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Fusion Proteins ◽  
Fusion Peptide ◽  
Loop Structure ◽  
Fusion Peptides ◽  
Enveloped Virus ◽  
Membrane Fusion Protein ◽  
Virus Fusion ◽  
Nonenveloped Virus

ABSTRACT The avian and Nelson Bay reoviruses are two of only a limited number of nonenveloped viruses capable of inducing cell-cell membrane fusion. These viruses encode the smallest known membrane fusion proteins (p10). We now show that a region of moderate hydrophobicity we call the hydrophobic patch (HP), present in the small N-terminal ectodomain of p10, shares the following characteristics with the fusion peptides of enveloped virus fusion proteins: (i) an abundance of glycine and alanine residues, (ii) a potential amphipathic secondary structure, (iii) membrane-seeking characteristics that correspond to the degree of hydrophobicity, and (iv) the ability to induce lipid mixing in a liposome fusion assay. The p10 HP is therefore predicted to provide a function in the mechanism of membrane fusion similar to those of the fusion peptides of enveloped virus fusion peptides, namely, association with and destabilization of opposing lipid bilayers. Mutational and biophysical analysis suggested that the internal fusion peptide of p10 lacks alpha-helical content and exists as a disulfide-stabilized loop structure. Similar kinked structures have been reported in the fusion peptides of several enveloped virus fusion proteins. The preservation of a predicted loop structure in the fusion peptide of this unusual nonenveloped virus membrane fusion protein supports an imperative role for a kinked fusion peptide motif in biological membrane fusion.

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