scholarly journals The Role of the Cytoplasmic Tail Region of Influenza Virus Hemagglutinin in Formation and Growth of Fusion Pores

Virology ◽  
1997 ◽  
Vol 235 (1) ◽  
pp. 118-128 ◽  
Author(s):  
Grigory B. Melikyan ◽  
Hong Jin ◽  
Robert A. Lamb ◽  
Fredric S. Cohen
Keyword(s):  
Influenza Virus ◽  
Cytoplasmic Tail ◽  
Tail Region ◽  
Influenza Virus Hemagglutinin ◽  
Fusion Pores

scholarly journals Role of Hemagglutinin Surface Density in the Initial Stages of Influenza Virus Fusion: Lack of Evidence for Cooperativity

2000 ◽  
Vol 74 (6) ◽  
pp. 2714-2720 ◽  
Author(s):  
Susanne Günther-Ausborn ◽  
Pieter Schoen ◽  
Ingrid Bartoldus ◽  
Jan Wilschut ◽  
Toon Stegmann
Keyword(s):  
Influenza Virus ◽  
Surface Density ◽  
Initial Rate ◽  
Fusion Activity ◽  
Cooperative Action ◽  
Lipid Ratio ◽  
Virus Fusion ◽  
Influenza Virus Hemagglutinin ◽  
Optimal Fusion

ABSTRACT Membrane fusion mediated by influenza virus hemagglutinin (HA) is believed to proceed via the cooperative action of multiple HA trimers. To determine the minimal number of HA trimers required to trigger fusion, and to assess the importance of cooperativity between these HA trimers, we have generated virosomes containing coreconstituted HAs derived from two strains of virus with different pH dependencies for fusion, X-47 (optimal fusion at pH 5.1; threshold at pH 5.6) and A/Shangdong (optimal fusion at pH 5.6; threshold at pH 6.0), and measured fusion of these virosomes with erythrocyte ghosts by a fluorescence lipid mixing assay. Virosomes with different X-47-to-A/Shangdong HA ratios, at a constant HA-to-lipid ratio, showed comparable ghost-binding activities, and the low-pH-induced conformational change of A/Shangdong HA did not affect the fusion activity of X-47 HA. The initial rate of fusion of these virosomes at pH 5.7 increased directly proportional to the surface density of A/Shangdong HA, and a single A/Shangdong trimer per virosome appeared to suffice to induce fusion. The reciprocal of the lag time before the onset of fusion was directly proportional to the surface density of fusion-competent HA. These results support the notion that there is no cooperativity between HA trimers during influenza virus fusion.

scholarly journals Effect of Cytoplasmic Tail Truncations on the Activity of the M2 Ion Channel of Influenza A Virus

1999 ◽  
Vol 73 (12) ◽  
pp. 9695-9701 ◽  
Author(s):  
Kurt Tobler ◽  
Marie L. Kelly ◽  
Lawrence H. Pinto ◽  
Robert A. Lamb
Keyword(s):  
Ion Channel ◽  
Influenza A Virus ◽  
Influenza A ◽  
Transmembrane Domain ◽  
Stop Codon ◽  
Specific Inhibitor ◽  
Cytoplasmic Tail ◽  
Proton Channel ◽  
Tail Region

ABSTRACT The M2 protein of influenza A virus forms a proton channel that is required for viral replication. The M2 ion channel is a homotetramer and has a 24-residue N-terminal extracellular domain, a 19-residue transmembrane domain, and a 54-residue cytoplasmic tail. We show here that the N-terminal methionine residue is cleaved from the mature protein. Translational stop codons were introduced into the M2 cDNA at residues 46, 52, 62, 72, 77, 82, 87, and 92. The deletion mutants were designated truncx, according to the amino acid position that was changed to a stop codon. We studied the role of the cytoplasmic tail by measuring the ion channel activity (the current sensitive to the M2-specific inhibitor amantadine) of the cytoplasmic tail truncation mutants expressed in oocytes of Xenopus laevis. When their conductance was measured over time, mutants trunc72, trunc77, and trunc92 behaved comparably to wild-type M2 protein (a decrease of only 4% over 30 min). In contrast, conductance decreased by 28% for trunc82, 27% for trunc62, and 81% for trunc52 channels. Complete closure of the channel could be observed in some cells for trunc62 and trunc52 within 30 min. These data suggest that a role of the cytoplasmic tail region of the M2 ion channel is to stabilize the pore against premature closure while the ectodomain is exposed to low pH.

scholarly journals Amino Acid Sequence Requirements of the Transmembrane and Cytoplasmic Domains of Influenza Virus Hemagglutinin for Viable Membrane Fusion

1999 ◽  
Vol 10 (6) ◽  
pp. 1821-1836 ◽  
Author(s):  
Grigory B. Melikyan ◽  
Sasa Lin ◽  
Michael G. Roth ◽  
Fredric S. Cohen
Keyword(s):  
Influenza Virus ◽  
Amino Acid ◽  
Amino Acid Sequence ◽  
Membrane Fusion ◽  
Integral Membrane Protein ◽  
Wild Type ◽  
Influenza Virus Hemagglutinin ◽  
Tm Domain ◽  
Fusion Pores ◽  
Sequence Requirements

The amino acid sequence requirements of the transmembrane (TM) domain and cytoplasmic tail (CT) of the hemagglutinin (HA) of influenza virus in membrane fusion have been investigated. Fusion properties of wild-type HA were compared with those of chimeras consisting of the ectodomain of HA and the TM domain and/or CT of polyimmunoglobulin receptor, a nonviral integral membrane protein. The presence of a CT was not required for fusion. But when a TM domain and CT were present, fusion activity was greater when they were derived from the same protein than derived from different proteins. In fact, the chimera with a TM domain of HA and truncated CT of polyimmunoglobulin receptor did not support full fusion, indicating that the two regions are not functionally independent. Despite the fact that there is wide latitude in the sequence of the TM domain that supports fusion, a point mutation of a semiconserved residue within the TM domain of HA inhibited fusion. The ability of a foreign TM domain to support fusion contradicts the hypothesis that a pore is composed solely of fusion proteins and supports the theory that the TM domain creates fusion pores after a stage of hemifusion has been achieved.

scholarly journals Modulation of cell surface transport and lipid raft localization by the cytoplasmic tail of the influenza virus hemagglutinin

2015 ◽  
Vol 18 (1) ◽  
pp. 125-136 ◽  
Author(s):  
Silvia Scolari ◽  
Katharina Imkeller ◽  
Fabian Jolmes ◽  
Michael Veit ◽  
Andreas Herrmann ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Cell Surface ◽  
Lipid Raft ◽  
Cytoplasmic Tail ◽  
Surface Transport ◽  
Influenza Virus Hemagglutinin

scholarly journals Effects of Bacterial Microflora of the Lower Digestive Tract of Free-Range Waterfowl on Influenza Virus Activation

2011 ◽  
Vol 77 (12) ◽  
pp. 4119-4125 ◽  
Author(s):  
Marcus D. King ◽  
M. Neal Guentzel ◽  
Bernard P. Arulanandam ◽  
Adria A. Bodour ◽  
Vinayak Brahmakshatriya ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Influenza A ◽  
Bacterial Flora ◽  
Bacterial Isolates ◽  
Influenza Virus Hemagglutinin ◽  
Bacterial Protease ◽  
Viral Hemagglutinin ◽  
Wild Waterfowl

ABSTRACTProteolytic cleavage activation of influenza virus hemagglutinin (HA0) is required for cell entry via receptor-mediated endocytosis. Despite numerous studies describing bacterial protease-mediated influenza A viral activation in mammals, very little is known about the role of intestinal bacterial flora of birds in hemagglutinin cleavage/activation. Therefore, the cloaca of wild waterfowl was examined for (i) representative bacterial types and (ii) their ability to cleave in a “trypsin-like” manner the precursor viral hemagglutinin molecule (HA0). Using radiolabeled HA0, bacterial secretion-mediated trypsin-like conversion of HA0 to HA1 and HA2 peptide products was observed to various degrees in 42 of 44 bacterial isolates suggestive of influenza virus activation in the cloaca of wild waterfowl. However, treatment of uncleaved virus with all bacterial isolates gave rise to substantially reduced emergent virus progeny compared with what was expected. Examination of two isolates exhibiting pronounced trypsin-like conversion of HA0 to HA1 and HA2 peptide products and low infectivity revealed lipase activity to be present. Because influenza virus possesses a complex lipid envelope, the presence of lipid hydrolase activity could in part account for the observed less-than-expected level of viable progeny. A thorough characterization of respective isolate protease HA0 hydrolysis products as well as other resident activities (i.e., lipase) is ongoing such that the role of these respective contributors in virus activation/inactivation can be firmly established.

scholarly journals Class II fusion protein of alphaviruses drives membrane fusion through the same pathway as class I proteins

2005 ◽  
Vol 169 (1) ◽  
pp. 167-177 ◽  
Author(s):  
Elena Zaitseva ◽  
Aditya Mittal ◽  
Diane E. Griffin ◽  
Leonid V. Chernomordik
Keyword(s):  
Influenza Virus ◽  
Fusion Proteins ◽  
Low Ph ◽  
Viral Fusion ◽  
Fusion Reactions ◽  
Influenza Virus Hemagglutinin ◽  
Viral Fusion Proteins ◽  
The Difference ◽  
Fusion Pores ◽  
Specific Inhibitors

Viral fusion proteins of classes I and II differ radically in their initial structures but refold toward similar conformations upon activation. Do fusion pathways mediated by alphavirus E1 and influenza virus hemagglutinin (HA) that exemplify classes II and I differ to reflect the difference in their initial conformations, or concur to reflect the similarity in the final conformations? Here, we dissected the pathway of low pH–triggered E1-mediated cell–cell fusion by reducing the numbers of activated E1 proteins and by blocking different fusion stages with specific inhibitors. The discovered progression from transient hemifusion to small, and then expanding, fusion pores upon an increase in the number of activated fusion proteins parallels that established for HA-mediated fusion. We conclude that proteins as different as E1 and HA drive fusion through strikingly similar membrane intermediates, with the most energy-intensive stages following rather than preceding hemifusion. We propose that fusion reactions catalyzed by all proteins of both classes follow a similar pathway.

scholarly journals Acylation-Mediated Membrane Anchoring of Avian Influenza Virus Hemagglutinin Is Essential for Fusion Pore Formation and Virus Infectivity

2005 ◽  
Vol 79 (10) ◽  
pp. 6449-6458 ◽  
Author(s):  
Ralf Wagner ◽  
Astrid Herwig ◽  
Nahid Azzouz ◽  
Hans Dieter Klenk
Keyword(s):  
Influenza Virus ◽  
Wild Type Virus ◽  
Fusion Pore ◽  
Cysteine Residues ◽  
Virus Infectivity ◽  
Wild Type ◽  
Protein Patterns ◽  
Virus Growth ◽  
Influenza Virus Hemagglutinin ◽  
Fusion Pores

ABSTRACT Attachment of palmitic acid to cysteine residues is a common modification of viral glycoproteins. The influenza virus hemagglutinin (HA) has three conserved cysteine residues at its C terminus serving as acylation sites. To analyze the structural and functional roles of acylation, we have generated by reverse genetics a series of mutants (Ac1, Ac2, and Ac3) of fowl plague virus (FPV) containing HA in which the acylation sites at positions 551, 559, and 562, respectively, have been abolished. When virus growth in CV1 and MDCK cells was analyzed, similar amounts of virus particles were observed with the mutants and the wild type. Protein patterns and lipid compositions, characterized by high cholesterol and glycolipid contents, were also indistinguishable. However, compared to wild-type virus, Ac2 and Ac3 virions were 10 and almost 1,000 times less infectious, respectively. Fluorescence transfer experiments revealed that loss of acyl chains impeded formation of fusion pores, whereas hemifusion was not affected. When the affinity to detergent-insoluble glycolipid (DIG) domains was analyzed by Triton X-100 treatment of infected cells and virions, solubilization of Ac2 and Ac3 HAs was markedly facilitated. These observations show that acylation of the cytoplasmic tail, while not necessary for targeting to DIG domains, promotes the firm anchoring and retention of FPV HA in these domains. They also indicate that tight DIG association of FPV HA is essential for formation of fusion pores and thus probably for infectivity.

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