scholarly journals Mutations in Pseudorabies Virus Glycoproteins gB, gD, and gH Functionally Compensate for the Absence of gL

2015 ◽  
Vol 90 (5) ◽  
pp. 2264-2272 ◽  
Author(s):  
Christina Schröter ◽  
Melina Vallbracht ◽  
Jan Altenschmidt ◽  
Sabrina Kargoll ◽  
Walter Fuchs ◽  
...  
Keyword(s):  
Amino Acid ◽  
Fusion Protein ◽  
Membrane Fusion ◽  
Pseudorabies Virus ◽  
Syncytium Formation ◽  
Single Amino Acid ◽  
Independent Experiment ◽  
Viral Glycoprotein ◽  
Bona Fide ◽  
Infectious Entry

ABSTRACTEntry of herpesviruses depends on the combined action of viral glycoprotein B (gB) and the heterodimeric gH/gL complex, which are activated by binding of the virion to specific cellular receptors. While gB carries signatures of a bona fide fusion protein, efficient membrane fusion requires gH/gL. However, although gB and gH/gL are essential for entry, the alphaherpesvirus pseudorabies virus (PrV) is capable of limited cell-to-cell spread in the absence of gL. To understand gH/gL function in more detail, the limited spread of PrV-ΔgL was used for reversion analyses by serial cell culture passages. In a first experiment, an infectious gL-negative mutant in which gL function was replaced by generation of a gD-gH hybrid protein was isolated (B. G. Klupp and T. C. Mettenleiter, J Virol 73:3014–3022, 1999). In a second, independent experiment PrV-ΔgLPassB4.1, which also replicated productively without gL, was isolated. Sequence analysis revealed mutations in gH but also in gB and gD. In a transfection-based fusion assay, two amino acid substitutions in the N-terminal part of gHB4.1(L70P and W103R) were found to be sufficient to compensate for lack of gL, while mutations present in gBB4.1enhanced fusogenicity. Coexpression of gBB4.1with the homologous gHB4.1resulted in strongly increased syncytium formation, which was further augmented by truncation of the gBB4.1C-terminal 29 amino acids. Nevertheless, gH was still required for membrane fusion. Surprisingly, coexpression of gDB4.1blocked syncytium formation in the fusion assays, which could be attributed to a V106A substitution within the ectodomain of gDB4.1.IMPORTANCEIn contrast to many other enveloped viruses, herpesviruses rely on the concerted action of four viral glycoproteins for membrane fusion during infectious entry. Although the highly conserved gB shows signatures of a fusion protein, for fusion induction it requires the gH/gL complex, whose role is still elusive. Here we demonstrated fusion activation by gH in the absence of gL after reversion analysis of gL-deleted pseudorabies virus. This gL-independent fusion activity depended on single amino acid exchanges affecting the gL-binding domain in gH, increasing fusogenicity in gB and allowing negative fusion regulation by gD. Thus, our results provide novel information on the interplay in the fusion machinery of herpesviruses.

scholarly journals A Functional F Analogue of Autographa californica Nucleopolyhedrovirus GP64 from the Agrotis segetum Granulovirus

2008 ◽  
Vol 82 (17) ◽  
pp. 8922-8926 ◽  
Author(s):  
Feifei Yin ◽  
Manli Wang ◽  
Ying Tan ◽  
Fei Deng ◽  
Just M. Vlak ◽  
...  
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Plutella Xylostella ◽  
Syncytium Formation ◽  
Low Ph ◽  
Autographa Californica ◽  
Agrotis Segetum ◽  
Induced Membrane ◽  
F Protein ◽  
Autographa Californica Nucleopolyhedrovirus

ABSTRACT The envelope fusion protein F of Plutella xylostella granulovirus is a computational analogue of the GP64 envelope fusion protein of Autographa californica nucleopolyhedrovirus (AcMNPV). Granulovirus (GV) F proteins were thought to be unable to functionally replace GP64 in the AcMNPV pseudotyping system. In the present study the F protein of Agrotis segetum GV (AgseGV) was identified experimentally as the first functional GP64 analogue from GVs. AgseF can rescue virion propagation and infectivity of gp64-null AcMNPV. The AgseF-pseudotyped AcMNPV also induced syncytium formation as a consequence of low-pH-induced membrane fusion.

Acquisition of NFKB1-selective DNA binding by substitution of four amino acid residues from NFKB1 into RelA

1993 ◽  
Vol 13 (7) ◽  
pp. 3850-3859
Author(s):  
T A Coleman ◽  
C Kunsch ◽  
M Maher ◽  
S M Ruben ◽  
C A Rosen
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Dna Binding ◽  
Fusion Protein ◽  
Binding Specificity ◽  
Single Amino Acid ◽  
Nf Kappa B ◽  
Dna Binding Specificity ◽  
Dna Motif ◽  
Single Amino Acid Change

The subunits of NF-kappa B, NFKB1 (formerly p50) and RelA (formerly p65), belong to a growing family of transcription factors that share extensive similarity to the c-rel proto-oncogene product. The homology extends over a highly conserved stretch of approximately 300 amino acids termed the Rel homology domain (RHD). This region has been shown to be involved in both multimerization (homo- and heterodimerization) and DNA binding. It is now generally accepted that homodimers of either subunit are capable of binding DNA that contains a kappa B site originally identified in the immunoglobulin enhancer. Recent studies have demonstrated that the individual subunits of the NF-kappa B transcription factor complex can be distinguished by their ability to bind distinct DNA sequence motifs. By using NFKB1 and RelA subunit fusion proteins, different regions within the RHD were found to confer DNA-binding and multimerization functions. A fusion protein that contains 34 N-terminal amino acids of NFKB1 and 264 amino acids of RelA displayed preferential binding to an NFKB1-selective DNA motif while dimerizing with the characteristics of RelA. Within the NFKB1 portion of this fusion protein, a single amino acid change of His to Arg altered the DNA-binding specificity to favor interaction with the RelA-selective DNA motif. Furthermore, substitution of four amino acids from NFKB1 into RelA was able to alter the DNA-binding specificity of the RelA protein to favor interaction with the NFKB1-selective site. Taken together, these findings demonstrate the presence of a distinct subdomain within the RHD involved in conferring the DNA-binding specificity of the Rel family of proteins.

scholarly journals A Single Amino Acid Change in the Newcastle Disease Virus Fusion Protein Alters the Requirement for HN Protein in Fusion

2000 ◽  
Vol 74 (11) ◽  
pp. 5101-5107 ◽  
Author(s):  
Theresa A. Sergel ◽  
Lori W. McGinnes ◽  
Trudy G. Morrison
Keyword(s):  
Amino Acid ◽  
Cell Surface ◽  
Protein Expression ◽  
Newcastle Disease ◽  
Amino Acid Change ◽  
Syncytium Formation ◽  
Single Amino Acid ◽  
Fusion Activity ◽  
Wild Type ◽  
Single Amino Acid Change

ABSTRACT The role of a leucine heptad repeat motif between amino acids 268 and 289 in the structure and function of the Newcastle disease virus (NDV) F protein was explored by introducing single point mutations into the F gene cDNA. The mutations affected either folding of the protein or the fusion activity of the protein. Two mutations, L275A and L282A, likely interfered with folding of the molecule since these proteins were not proteolytically cleaved, were minimally expressed at the cell surface, and formed aggregates. L268A mutant protein was cleaved and expressed at the cell surface although the protein migrated slightly slower than wild type on polyacrylamide gels, suggesting an alteration in conformation or processing. L268A protein was fusion inactive in the presence or absence of HN protein expression. Mutant L289A protein was expressed at the cell surface and proteolytically cleaved at better than wild-type levels. Most importantly, this protein mediated syncytium formation in the absence of HN protein expression although HN protein enhanced fusion activity. These results show that a single amino acid change in the F1 portion of the NDV F protein can alter the stringent requirement for HN protein expression in syncytium formation.

scholarly journals Determinants of Syncytium Formation in Microglia by Human Immunodeficiency Virus Type 1: Role of the V1/V2 Domains

2000 ◽  
Vol 74 (2) ◽  
pp. 693-701 ◽  
Author(s):  
Joseph T. C. Shieh ◽  
Julio Martín ◽  
Gordon Baltuch ◽  
Michael H. Malim ◽  
Francisco González-Scarano
Keyword(s):  
Human Immunodeficiency Virus ◽  
Amino Acid ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Single Amino Acid ◽  
Single Amino Acid Change ◽  
Immunodeficiency Virus ◽  
Hiv 1

ABSTRACT Microglia are the main reservoir for human immunodeficiency virus type 1 (HIV-1) in the central nervous system (CNS), and multinucleated giant cells, the result of fusion of HIV-1-infected microglia and brain macrophages, are the neuropathologic hallmark of HIV dementia. One potential explanation for the formation of syncytia is viral adaptation for these CD4+ CNS cells. HIV-1BORI-15, a virus adapted to growth in microglia by sequential passage in vitro, mediates high levels of fusion and replicates more efficiently in microglia and monocyte-derived-macrophages than its unpassaged parent (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. Gonzalez-Scarano, J. Virol. 70:7654–7662, 1996). Since the interaction between the viral envelope glycoprotein and CD4 and the chemokine receptor mediates fusion and plays a key role in tropism, we have analyzed the HIV-1BORI-15 env as a fusogen and in recombinant and pseudotyped viruses. Its syncytium-forming phenotype is not the result of a switch in coreceptor use but rather of the HIV-1BORI-15envelope-mediated fusion of CD4+CCR5+ cells with greater efficiency than that of its parental strain, either by itself or in the context of a recombinant virus. Genetic analysis indicated that the syncytium-forming phenotype was due to four discrete amino acid differences in V1/V2, with a single-amino-acid change between the parent and the adapted virus (E153G) responsible for the majority of the effect. Additionally, HIV-1BORI-15 env-pseudotyped viruses were less sensitive to decreases in the levels of CD4 on transfected 293T cells, leading to the hypothesis that the differences in V1/V2 alter the interaction between this envelope and CD4 or CCR5, or both. In sum, the characterization of the envelope of HIV-1BORI-15, a highly fusogenic glycoprotein with genetic determinants in V1/V2, may lead to a better understanding of the relationship between HIV replication and syncytium formation in the CNS and of the importance of this region of gp120 in the interaction with CD4 and CCR5.

scholarly journals Functional Relevance of the N-Terminal Domain of Pseudorabies Virus Envelope Glycoprotein H and Its Interaction with Glycoprotein L

2017 ◽  
Vol 91 (9) ◽  
Author(s):  
Melina Vallbracht ◽  
Sascha Rehwaldt ◽  
Barbara G. Klupp ◽  
Thomas C. Mettenleiter ◽  
Walter Fuchs
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Receptor Binding ◽  
Pseudorabies Virus ◽  
Envelope Glycoproteins ◽  
Virus Envelope ◽  
Enveloped Viruses ◽  
Gh Gene ◽  
Functional Relevance

ABSTRACT Several envelope glycoproteins are involved in herpesvirus entry into cells, direct cell-to-cell spread, and induction of cell fusion. The membrane fusion protein glycoprotein B (gB) and the presumably gB-activating heterodimer gH/gL are essential for these processes and conserved throughout the Herpesviridae. However, after extended cell culture passage of gL-negative mutants of the alphaherpesvirus pseudorabies virus (PrV), phenotypic revertants could be isolated which had acquired spontaneous mutations affecting the gL-interacting N-terminal part of the gH ectodomain (gDH and gHB4.1) (B. G. Klupp and T. C. Mettenleiter, J Virol 73:3014–3022, 1999; C. Schröter, M. Vallbracht, J. Altenschmidt, S. Kargoll, W. Fuchs, B. G. Klupp, and T. C. Mettenleiter, J Virol 90:2264–2272, 2016). To investigate the functional relevance of this part of gH in more detail, we introduced an in-frame deletion of 66 codons at the 5′ end of the plasmid-cloned gH gene (gH32/98). The N-terminal signal peptide was retained, and the deletion did not affect expression or processing of gH but abrogated its function in in vitro fusion assays. Insertion of the engineered gH gene into the PrV genome resulted in a defective mutant (pPrV-gH32/98K), which was incapable of entry and spread. Interestingly, in vitro activity of mutated gH32/98 was restored when it was coexpressed with hyperfusogenic gBB4.1, obtained from a passaged gL deletion mutant of PrV. Moreover, the entry and spread defects of pPrV-gH32/98K were compensated by the mutations in gBB4.1 in cis, as well as in trans, independent of gL. Thus, PrV gL and the gL-interacting domain of gH are not strictly required for function. IMPORTANCE Membrane fusion is crucial for infectious entry and spread of enveloped viruses. While many enveloped viruses require only one or two proteins for receptor binding and membrane fusion, herpesvirus infection depends on several envelope glycoproteins. Besides subfamily-specific receptor binding proteins, the core fusion machinery consists of the conserved fusion protein gB and the gH/gL complex. The role of the latter is unclear, but it is hypothesized to interact with gB for fusion activation. Using isogenic virus recombinants, we demonstrate here that gL and the gL-binding domain of PrV gH are not strictly required for membrane fusion during virus entry and spread when concomitantly mutations in gB are present which increase its fusogenicity. Thus, our results strongly support the notion of a functional gB-gH interaction during the fusion process.

scholarly journals Palmitoylation, Membrane-Proximal Basic Residues, and Transmembrane Glycine Residues in the Reovirus p10 Protein Are Essential for Syncytium Formation

2003 ◽  
Vol 77 (18) ◽  
pp. 9769-9779 ◽  
Author(s):  
Maya Shmulevitz ◽  
Jayme Salsman ◽  
Roy Duncan
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Transmembrane Domain ◽  
Nonstructural Protein ◽  
Fusion Reaction ◽  
Specific Interaction ◽  
Syncytium Formation ◽  
Surface Expression ◽  
Fusion Activity ◽  
Basic Region

ABSTRACT Avian reovirus and Nelson Bay reovirus are two unusual nonenveloped viruses that induce extensive cell-cell fusion via expression of a small nonstructural protein, termed p10. We investigated the importance of the transmembrane domain, a conserved membrane-proximal dicysteine motif, and an endodomain basic region in the membrane fusion activity of p10. We now show that the p10 dicysteine motif is palmitoylated and that loss of palmitoylation correlates with a loss of fusion activity. Mutational and functional analyses also revealed that a triglycine motif within the transmembrane domain and the membrane-proximal basic region were essential for p10-mediated membrane fusion. Mutations in any of these three motifs did not influence events upstream of syncytium formation, such as p10 membrane association, protein topology, or surface expression, suggesting that these motifs are more intimately associated with the membrane fusion reaction. These results suggest that the rudimentary p10 fusion protein has evolved a mechanism of inducing membrane merger that is highly dependent on the specific interaction of several different motifs with donor membranes. In addition, cross-linking, coimmunoprecipitation, and complementation assays provided no evidence for p10 homo- or heteromultimer formation, suggesting that p10 may be the first example of a membrane fusion protein that does not form stable, higher-order multimers.

scholarly journals Cell-Cell Fusion Induced by the Avian Reovirus Membrane Fusion Protein Is Regulated by Protein Degradation

2004 ◽  
Vol 78 (11) ◽  
pp. 5996-6004 ◽  
Author(s):  
Maya Shmulevitz ◽  
Jennifer Corcoran ◽  
Jayme Salsman ◽  
Roy Duncan
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Cell Fusion ◽  
Transmembrane Protein ◽  
Syncytium Formation ◽  
Replication Cycle ◽  
Stable Form ◽  
Avian Reovirus ◽  
Membrane Fusion Protein ◽  
Cell Cell

ABSTRACT The p10 fusion-associated small transmembrane protein of avian reovirus induces extensive syncytium formation in transfected cells. Here we show that p10-induced cell-cell fusion is restricted by rapid degradation of the majority of newly synthesized p10. The small ectodomain of p10 targets the protein for degradation following p10 insertion into an early membrane compartment. Paradoxically, conservative amino acid substitutions in the p10 ectodomain hydrophobic patch that eliminate fusion activity also increase p10 stability. The small amount of p10 that escapes intracellular degradation accumulates at the cell surface in a relatively stable form, where it mediates cell-cell fusion as a late-stage event in the virus replication cycle. The unusual relationship between a nonstructural viral membrane fusion protein and the replication cycle of a nonenveloped virus has apparently contributed to the evolution of a novel mechanism for restricting the extent of virus-induced cell-cell fusion.

scholarly journals Analysis of receptor (CD46, CD150) usage by measles virus

2002 ◽  
Vol 83 (6) ◽  
pp. 1431-1436 ◽  
Author(s):  
Christian Erlenhöfer ◽  
W. Paul Duprex ◽  
Bert K. Rima ◽  
Volker ter Meulen ◽  
Jürgen Schneider-Schaulies
Keyword(s):  
Amino Acid ◽  
Measles Virus ◽  
Syncytium Formation ◽  
Single Amino Acid ◽  
Wild Type ◽  
Recombinant Viruses ◽  
Common Receptor ◽  
A Minor ◽  
Acid Alteration ◽  
Type Strains

In order to investigate which measles virus (MV)-strains use CD46 and/or CD150 (signalling lymphocytic activation molecule, SLAM) as receptors, CHO cells expressing either recombinant CD46 or SLAM were infected with a panel of 28 MV-strains including vaccine strains, wild-type strains with various passage histories and recombinant viruses. We found that SLAM served as a common receptor conferring virus uptake and syncytium formation for all MV-strains tested. Predominantly vaccine and laboratory adapted strains, but also a minor fraction of the wild-type strains tested, could utilize both CD46 and SLAM. Using recombinant viruses, we demonstrate that the single amino acid exchange in the haemagglutinin (H) protein at position 481 Asn/Tyr (H481NY) determines whether the virus can utilize CD46. This amino acid alteration has no affect on the usage of SLAM as receptor, and as such demonstrates that the binding sites for SLAM and CD46 are distinct.

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