scholarly journals Reverse Engineering Provides Insights on the Evolution of Subgroups A to E Avian Sarcoma and Leukosis Virus Receptor Specificity

Viruses ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 497 ◽  
Author(s):  
Mark J. Federspiel
Keyword(s):  
Reverse Engineering ◽  
Conformational Changes ◽  
Envelope Glycoprotein ◽  
Genetic Selection ◽  
Experimental System ◽  
Initial Step ◽  
Cellular Protein ◽  
Viral Fusion ◽  
Virus Envelope ◽  
Avian Sarcoma

The initial step of retrovirus entry—the interaction between the virus envelope glycoprotein trimer and a cellular receptor—is complex, involving multiple, noncontiguous determinants in both proteins that specify receptor choice, binding affinity and the ability to trigger conformational changes in the viral glycoproteins. Despite the complexity of this interaction, retroviruses have the ability to evolve the structure of their envelope glycoproteins to use a different cellular protein as receptors. The highly homologous subgroup A to E Avian Sarcoma and Leukosis Virus (ASLV) glycoproteins belong to the group of class 1 viral fusion proteins with a two-step triggering mechanism that allows experimental access to intermediate structures during the fusion process. We and others have taken advantage of replication-competent ASLVs and exploited genetic selection strategies to force the ASLVs to naturally evolve and acquire envelope glycoprotein mutations to escape the pressure on virus entry and still yield a functional replicating virus. This approach allows for the simultaneous selection of multiple mutations in multiple functional domains of the envelope glycoprotein that may be required to yield a functional virus. Here, we review the ASLV family and experimental system and the reverse engineering approaches used to understand the evolution of ASLV receptor usage.

scholarly journals Role of Hydrophobic Residues in the Central Ectodomain of gp41 in Maintaining the Association between Human Immunodeficiency Virus Type 1 Envelope Glycoprotein Subunits gp120 and gp41

2004 ◽  
Vol 78 (9) ◽  
pp. 4921-4926 ◽  
Author(s):  
Joanne York ◽  
Jack H. Nunberg
Keyword(s):  
Human Immunodeficiency Virus ◽  
Conformational Changes ◽  
Envelope Glycoprotein ◽  
Site Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Virus Envelope ◽  
Hydrophobic Residues ◽  
Immunodeficiency Virus ◽  
Mediate Cell ◽  
The Stability

ABSTRACT The interaction between the gp120 and gp41 subunits of the human immunodeficiency virus envelope glycoprotein serves to stabilize the virion form of the complex and to transmit receptor-induced conformational changes in gp120 to trigger the membrane fusion activity of gp41. In this study, we used site-directed mutagenesis to identify amino acid residues in the central ectodomain of gp41 that contribute to the stability of the gp120-gp41 association. We identified alanine mutations at six positions, including four tryptophan residues, which result in mutant envelope glycoprotein complexes that fail to retain gp120 on the cell surface. These envelope glycoproteins readily shed their gp120 and are unable to mediate cell-cell fusion. These findings suggest an important role for the conserved bulky hydrophobic residues in stabilizing the gp120-gp41 complex.

scholarly journals Conformational changes induced in the human immunodeficiency virus envelope glycoprotein by soluble CD4 binding.

1991 ◽  
Vol 174 (2) ◽  
pp. 407-415 ◽  
Author(s):  
Q J Sattentau ◽  
J P Moore
Keyword(s):  
Human Immunodeficiency Virus ◽  
Receptor Binding ◽  
Conformational Changes ◽  
Envelope Glycoprotein ◽  
Fusion Reaction ◽  
Cd4 Cells ◽  
Virus Envelope ◽  
Sequence Of Events ◽  
Immunodeficiency Virus ◽  
Infected Cells

The human immunodeficiency virus (HIV) binds to the surface of T lymphocytes and other cells of the immune system via a high affinity interaction between CD4 and the HIV outer envelope glycoprotein, gp120. By analogy with certain other enveloped viruses, receptor binding by HIV may be followed by exposure of the hydrophobic NH2 terminus of its transmembrane glycoprotein, gp41, and fusion of the virus and cell membranes. A similar sequence of events is thought to take place between HIV-infected and uninfected CD4+ cells, resulting in their fusion to form syncytia. In this study, we have used a soluble, recombinant form of CD4 (sCD4) to model events taking place after receptor binding by the HIV envelope glycoproteins. We demonstrate that the complexing of sCD4 with gp120 induces conformational changes within envelope glycoprotein oligomers. This was measured on HIV-1-infected cells by the increased binding of antibodies to the gp120/V3 loops, and on the surface of virions by increased cleavage of this loop by an exogenous proteinase. At 37 degrees C, these conformational changes are coordinate with the dissociation of gp120/sCD4 complexes from gp41, and the increased exposure of gp41 epitopes. At 4 degrees C, gp120 dissociation from the cell surface does not occur, but increased exposure of both gp120/V3 and gp41 epitopes is detected. We propose that these events occurring after CD4 binding are integral components of the membrane fusion reaction between HIV or HIV-infected cells and CD4+ cells.

Avian sarcoma virus envelope glycoprotein (gp85) specifically binds chick embryo fibroblasts

Virology ◽  
1979 ◽  
Vol 97 (2) ◽  
pp. 448-453 ◽  
Author(s):  
C.F. Moldow ◽  
F.H. Reynolds ◽  
J. Lake ◽  
K. Lundberg ◽  
J.R. Stephensonv
Keyword(s):  
Chick Embryo ◽  
Envelope Glycoprotein ◽  
Avian Sarcoma Virus ◽  
Virus Envelope ◽  
Sarcoma Virus ◽  
Embryo Fibroblasts ◽  
Avian Sarcoma

scholarly journals An Antibody Directed against the Fusion Peptide of Junín Virus Envelope Glycoprotein GPC Inhibits pH-Induced Membrane Fusion

2010 ◽  
Vol 84 (12) ◽  
pp. 6119-6129 ◽  
Author(s):  
Joanne York ◽  
Jody D. Berry ◽  
Ute Ströher ◽  
Qunnu Li ◽  
Heinz Feldmann ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Membrane Fusion ◽  
Host Cell ◽  
Envelope Glycoprotein ◽  
Fusion Peptide ◽  
Intermediate Form ◽  
Viral Fusion ◽  
Virus Envelope ◽  
Host Cell Membrane ◽  
Helix Bundle

ABSTRACT The arenavirus envelope glycoprotein (GPC) initiates infection in the host cell through pH-induced fusion of the viral and endosomal membranes. As in other class I viral fusion proteins, this process proceeds through a structural reorganization in GPC in which the ectodomain of the transmembrane fusion subunit (G2) engages the host cell membrane and subsequently refolds to form a highly stable six-helix bundle structure that brings the two membranes into apposition for fusion. Here, we describe a G2-directed monoclonal antibody, F100G5, that prevents membrane fusion by binding to an intermediate form of the protein on the fusion pathway. Inhibition of syncytium formation requires that F100G5 be present concomitant with exposure of GPC to acidic pH. We show that F100G5 recognizes neither the six-helix bundle nor the larger trimer-of-hairpins structure in the postfusion form of G2. Rather, Western blot analysis using recombinant proteins and a panel of alanine-scanning GPC mutants revealed that F100G5 binding is dependent on an invariant lysine residue (K283) near the N terminus of G2, in the so-called fusion peptide that inserts into the host cell membrane during the fusion process. The F100G5 epitope is located in the internal segment of the bipartite GPC fusion peptide, which also contains four conserved cysteine residues, raising the possibility that this fusion peptide may be highly structured. Collectively, our studies indicate that F100G5 identifies an on-path intermediate form of GPC. Binding to the transiently exposed fusion peptide may interfere with G2 insertion into the host cell membrane. Strategies to effectively target fusion peptide function in the endosome may lead to novel classes of antiviral agents.

scholarly journals Critical Role for the Cysteines Flanking the Internal Fusion Peptide of Avian Sarcoma/Leukosis Virus Envelope Glycoprotein

2000 ◽  
Vol 74 (20) ◽  
pp. 9738-9741 ◽  
Author(s):  
S. E. Delos ◽  
J. M. White
Keyword(s):  
Cell Fusion ◽  
Disulfide Bond ◽  
Envelope Glycoprotein ◽  
Ebola Virus ◽  
Leukemia Virus ◽  
Critical Role ◽  
Fusion Peptide ◽  
Virus Envelope ◽  
Mediate Cell ◽  
Avian Sarcoma

ABSTRACT The transmembrane subunit (TM) of the envelope glycoprotein (Env) of the oncovirus avian sarcoma/leukosis virus (ASLV) contains an internal fusion peptide flanked by two cysteines (C9 and C45). These cysteines, as well as an analogous pair in the Ebola virus GP glycoprotein, are predicted to be joined by a disulfide bond. To examine the importance of these cysteines, we mutated C9 and C45 in the ASLV subtype A Env (EnvA), individually and together, to serine. All of the mutant EnvAs formed trimers that were composed of the proteolytically processed surface (SU) and TM subunits. All mutant EnvAs were incorporated into murine leukemia virus pseudotyped virions and bound receptor with wild-type affinity. Nonetheless, all mutant EnvAs were significantly impaired (∼1,000-fold) in their ability to support infectivity. They were also significantly impaired in their ability to mediate cell-cell fusion. Our data are consistent with a model in which the internal fusion peptide of ASLV-A EnvA exists as a loop that is stabilized by a disulfide bond at its base and in which this stabilized loop serves an important function during virus-cell fusion. The fusion peptide of the Ebola virus GP glycoprotein may conform to a similar structure.

scholarly journals Identification of glycosylation sites in the SU component of the Avian Sarcoma/Leukosis virus Envelope Glycoprotein (Subgroup A) by mass spectrometry

Virology ◽  
2004 ◽  
Vol 326 (1) ◽  
pp. 171-181 ◽  
Author(s):  
Mamuka Kvaratskhelia ◽  
Patrick K Clark ◽  
Sonja Hess ◽  
Deborah C Melder ◽  
Mark J Federspiel ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Envelope Glycoprotein ◽  
Virus Envelope ◽  
Glycosylation Sites ◽  
Avian Sarcoma

scholarly journals Avian Sarcoma and Leukosis Virus Envelope Glycoproteins Evolve to Broaden Receptor Usage Under Pressure from Entry Competitors †

Viruses ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 519 ◽  
Author(s):  
Audelia Munguia ◽  
Mark J. Federspiel
Keyword(s):  
Binding Affinity ◽  
Genetic Selection ◽  
Hypervariable Region ◽  
Surface Proteins ◽  
Soluble Form ◽  
Envelope Glycoproteins ◽  
Virus Envelope ◽  
Receptor Usage ◽  
Hypervariable Regions ◽  
Avian Sarcoma

The subgroup A through E avian sarcoma and leukosis viruses (ASLV(A) through ASLV(E)) are a group of highly related alpharetroviruses that have evolved their envelope glycoproteins to use different receptors to enable efficient virus entry due to host resistance and/or to expand host range. Previously, we demonstrated that ASLV(A) in the presence of a competitor to the subgroup A Tva receptor, SUA-rIgG immunoadhesin, evolved to use other receptor options. The selected mutant virus, RCASBP(A)Δ155–160, modestly expanded its use of the Tvb and Tvc receptors and possibly other cell surface proteins while maintaining the binding affinity to Tva. In this study, we further evolved the Δ155–160 virus with the genetic selection pressure of a soluble form of the Tva receptor that should force the loss of Tva binding affinity in the presence of the Δ155–160 mutation. Viable ASLVs were selected that acquired additional mutations in the Δ155–160 Env hypervariable regions that significantly broadened receptor usage to include Tvb and Tvc as well as retaining the use of Tva as a receptor determined by receptor interference assays. A similar deletion in the hr1 hypervariable region of the subgroup C ASLV glycoproteins evolved to broaden receptor usage when selected on Tvc-negative cells.

scholarly journals Sindbis Virus Entry into Cells Triggers Apoptosis by Activating Sphingomyelinase, Leading to the Release of Ceramide

2000 ◽  
Vol 74 (14) ◽  
pp. 6425-6432 ◽  
Author(s):  
Jia-Tsrong Jan ◽  
Subroto Chatterjee ◽  
Diane E. Griffin
Keyword(s):  
Conformational Changes ◽  
Sindbis Virus ◽  
Virus Entry ◽  
Neuroblastoma Cells ◽  
Cellular Protein ◽  
Acid Ceramidase ◽  
Virus Envelope ◽  
Endosomal Membrane ◽  
Induced Apoptosis ◽  
Viral Surface

ABSTRACT Sindbis virus (SV) causes acute encephalomyelitis by infecting and inducing the death of neurons. Induction of apoptosis occurs during virus entry and involves acid-induced conformational changes in the viral surface glycoproteins and sphingomyelin (SM)-dependent fusion of the virus envelope with the endosomal membrane. We have studied neuroblastoma cells to determine how this entry process triggers cell death. Acidic sphingomyelinase was activated during entry followed by activation of neutral sphingomyelinase, SM degradation, and a sustained increase in ceramide. Ceramide-induced apoptosis and SV-induced apoptosis could be inhibited by treatment with Z-VAD-fmk, a caspase inhibitor, and by overexpression of Bcl-2, an antiapoptotic cellular protein. Acid ceramidase, expressed in a recombinant SV, decreased intracellular ceramide and protected cells from apoptosis. The data suggest that acid-induced SM-dependent virus fusion initiates the apoptotic cascade by inducing SM degradation and ceramide release.

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