Electrostatic Architecture of the Infectious Salmon Anemia Virus (ISAV) Core Fusion Protein Illustrates a Carboxyl-Carboxylate pH Sensor

Cook, Jonathan D.; Soto-Montoya, Hazel; Korpela, Markus K.; Lee, Jeffrey E.

doi:10.1074/jbc.m115.644781

Cited by 12 publications

(7 citation statements)

References 47 publications

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“…Traversing the endosomal pathway introduces the dissociated ISAV F protein to a steady decrease in pH, which is the final, irreversible signal for ISAV F protein rearrangement, consistent with previous studies that ISAV F is stabilized in its postfusion conformation at low pH (30). Interestingly, the expression of ISAV F on the surface of cultured cells is sufficient for syncytia formation when these cells are exposed to low-pH media (31).…”

Section: -Oassupporting

confidence: 89%

Structure of the infectious salmon anemia virus receptor complex illustrates a unique binding strategy for attachment

Cook

Sultana

Lee

2017

Proc. Natl. Acad. Sci. U.S.A.

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Orthomyxoviruses are an important family of RNA viruses, which include the various influenza viruses. Despite global efforts to eradicate orthomyxoviral pathogens, these infections remain pervasive. One such orthomyxovirus, infectious salmon anemia virus (ISAV), spreads easily throughout farmed and wild salmonids, constituting a significant economic burden. ISAV entry requires the interplay of the virion-attached hemagglutinin-esterase and fusion glycoproteins. Preventing infections will rely on improved understanding of ISAV entry. Here, we present the crystal structures of ISAV hemagglutinin-esterase unbound and complexed with receptor. Several distinctive features observed in ISAV HE are not seen in any other viral glycoprotein. The structures reveal a unique mode of receptor binding that is dependent on the oligomeric assembly of hemagglutinin-esterase. Importantly, ISAV hemagglutininesterase receptor engagement does not initiate conformational rearrangements, suggesting a distinct viral entry mechanism. This work improves our understanding of ISAV pathogenesis and expands our knowledge on the overall diversity of viral glycoprotein-mediated entry mechanisms. Finally, it provides an atomic-resolution model of the primary neutralizing antigen critical for vaccine development.orthomyxovirus | viral fusion | viral attachment | hemagglutinin | infectious salmon anemia virus

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Section: -Oassupporting

confidence: 89%

Structure of the infectious salmon anemia virus receptor complex illustrates a unique binding strategy for attachment

Cook

Sultana

Lee

2017

Proc. Natl. Acad. Sci. U.S.A.

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“…In other viruses, this stimulus induces major F protein structural rearrangements and the assembly of the head-domain heptad repeats into a central, trimeric α-helical coiled coil structure that propel the fusion peptide towards the target membrane [84,98]. Recent structural analysis confirmed that in ISAV F protein, residues E327 and E329 carboxyl-carbonate acts as a pH sensor that once activated at low pH binds and stabilises the extended central coiled-coil region via strong short hydrogen bonds [45]. In the present study, both the full length and deleted HPR HE could potentially allow the proteolytic cleavage to take place.…”

Section: Discussionmentioning

confidence: 99%

“…The ISAV F is a pH-dependent class I membrane fusion protein which needs cleavage by a host proteolytic enzyme for activation [9,45]. The F protein is generated as a 50 kDa inactive precursor molecule (F0), which once cleaved results in two disulphide linked subunits, F1 and F2 at 30 and 20 kDa respectively [9].…”

Section: Introductionmentioning

confidence: 99%

Dual Mutation Events in the Haemagglutinin-Esterase and Fusion Protein from an Infectious Salmon Anaemia Virus HPR0 Genotype Promote Viral Fusion and Activation by an Ubiquitous Host Protease

et al. 2015

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In Infectious salmon anaemia virus (ISAV), deletions in the highly polymorphic region (HPR) in the near membrane domain of the haemagglutinin-esterase (HE) stalk, influence viral fusion. It is suspected that selected mutations in the associated Fusion (F) protein may also be important in regulating fusion activity. To better understand the underlying mechanisms involved in ISAV fusion, several mutated F proteins were generated from the Scottish Nevis and Norwegian SK779/06 HPR0. Co-transfection with constructs encoding HE and F were performed, fusion activity assessed by content mixing assay and the degree of proteolytic cleavage by western blot. Substitutions in Nevis F demonstrated that K276 was the most likely cleavage site in the protein. Furthermore, amino acid substitutions at three sites and two insertions, all slightly upstream of K276, increased fusion activity. Co-expression with HE harbouring a full-length HPR produced high fusion activities when trypsin and low pH were applied. In comparison, under normal culture conditions, groups containing a mutated HE with an HPR deletion were able to generate moderate fusion levels, while those with a full length HPR HE could not induce fusion. This suggested that HPR length may influence how the HE primes the F protein and promotes fusion activation by an ubiquitous host protease and/or facilitate subsequent post-cleavage refolding steps. Variations in fusion activity through accumulated mutations on surface glycoproteins have also been reported in other orthomyxoviruses and paramyxoviruses. This may in part contribute to the different virulence and tissue tropism reported for HPR0 and HPR deleted ISAV genotypes.

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“…As expected, ISAV M1 is expressed late during infection and accumulates in both nucleus and cytosol (25,26). A number of findings indicate that the overall organization of the ISA virion, including the viral RNP (27), the nucleoprotein (28), and the viral fusion machinery (29), shares a high level of structural homology to those of the influenza viruses.…”

mentioning

confidence: 88%

Crystal structure of an orthomyxovirus matrix protein reveals mechanisms for self-polymerization and membrane association

Zhang

Zheng

Toh

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Many enveloped viruses encode a matrix protein. In the influenza A virus, the matrix protein M1 polymerizes into a rigid protein layer underneath the viral envelope to help enforce the shape and structural integrity of intact viruses. The influenza virus M1 is also known to mediate virus budding as well as the nuclear export of the viral nucleocapsids and their subsequent packaging into nascent viral particles. Despite extensive studies on the influenza A virus M1 (FLUA-M1), only crystal structures of its N-terminal domain are available. Here we report the crystal structure of the full-length M1 from another orthomyxovirus that infects fish, the infectious salmon anemia virus (ISAV). The structure of ISAV-M1 assumes the shape of an elbow, with its N domain closely resembling that of the FLUA-M1. The C domain, which is connected to the N domain through a flexible linker, is made of four α-helices packed as a tight bundle. In the crystal, ISAV-M1 monomers form infinite 2D arrays with a network of interactions involving both the N and C domains. Results from liposome flotation assays indicated that ISAV-M1 binds membrane via electrostatic interactions that are primarily mediated by a positively charged surface loop from the N domain. Cryoelectron tomography reconstruction of intact ISA virions identified a matrix protein layer adjacent to the inner leaflet of the viral membrane. The physical dimensions of the virion-associated matrix layer are consistent with the 2D ISAV-M1 crystal lattice, suggesting that the crystal lattice is a valid model for studying M1-M1, M1-membrane, and M1-RNP interactions in the virion.A ll members of the Orthomyxoviridae family, including the influenza viruses A-D, thogotovirus, and isavirus, encode a matrix protein called M1. In the influenza A virus, M1 is produced by a colinear transcript made from the gene segment 7 (1). As one of the most abundantly made viral proteins, the influenza A virus M1 plays multiple roles during the virus life cycle. Upon viral entry, the acidification of the viral interior in the endosome weakens the interaction between M1 and the viral ribonucleoprotein complexes (vRNPs), thus allowing M1-free vRNPs to be imported to the nucleus for viral RNA replication and transcription (2, 3). As infection proceeds, newly synthesized M1 enters the nucleus to mediate the nuclear export of nascent vRNPs. A "daisy-chain" complex is formed with the vRNP binding to the C-terminal domain of M1 (4) and the N-terminal domain of M1 interacting with the nuclear export protein (NEP), also called NS2. Through its nuclear export signal (NES), NEP is specifically recognized by the cellular exportin Crm1, which then facilitates the transport of vRNPs across the nuclear membrane to the cytoplasm in a RanGTP-dependent manner (5). It has been shown that M1 binding to vRNP in the nucleus is able to block mRNA transcription (4, 6). In the cytosol, M1 interacts with the cytoplasmic tails of the glycoproteins HA and NA. Such interactions promote M1 association with lipid raft membranes and...

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Electrostatic Architecture of the Infectious Salmon Anemia Virus (ISAV) Core Fusion Protein Illustrates a Carboxyl-Carboxylate pH Sensor

Cited by 12 publications

References 47 publications

Structure of the infectious salmon anemia virus receptor complex illustrates a unique binding strategy for attachment

Structure of the infectious salmon anemia virus receptor complex illustrates a unique binding strategy for attachment

Dual Mutation Events in the Haemagglutinin-Esterase and Fusion Protein from an Infectious Salmon Anaemia Virus HPR0 Genotype Promote Viral Fusion and Activation by an Ubiquitous Host Protease

Crystal structure of an orthomyxovirus matrix protein reveals mechanisms for self-polymerization and membrane association

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