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      New World Bats Harbor Diverse Influenza A Viruses

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          Abstract

          Aquatic birds harbor diverse influenza A viruses and are a major viral reservoir in nature. The recent discovery of influenza viruses of a new H17N10 subtype in Central American fruit bats suggests that other New World species may similarly carry divergent influenza viruses. Using consensus degenerate RT-PCR, we identified a novel influenza A virus, designated as H18N11, in a flat-faced fruit bat ( Artibeus planirostris) from Peru. Serologic studies with the recombinant H18 protein indicated that several Peruvian bat species were infected by this virus. Phylogenetic analyses demonstrate that, in some gene segments, New World bats harbor more influenza virus genetic diversity than all other mammalian and avian species combined, indicative of a long-standing host-virus association. Structural and functional analyses of the hemagglutinin and neuraminidase indicate that sialic acid is not a ligand for virus attachment nor a substrate for release, suggesting a unique mode of influenza A virus attachment and activation of membrane fusion for entry into host cells. Taken together, these findings indicate that bats constitute a potentially important and likely ancient reservoir for a diverse pool of influenza viruses.

          Author Summary

          Previous studies indicated that a novel influenza A virus (H17N10) was circulating in fruit bats from Guatemala (Central America). Herein, we investigated whether similar viruses are present in bat species from South America. Analysis of rectal swabs from bats sampled in the Amazon rainforest region of Peru identified another new influenza A virus from bats that is phylogenetically distinct from the one identified in Guatemala. The genes that encode the surface proteins of the new virus from the flat-faced fruit bat were designated as new subtype H18N11. Serologic testing of blood samples from several species of Peruvian bats indicated a high prevalence of antibodies to the surface proteins. Phylogenetic analyses demonstrate that bat populations from Central and South America maintain as much influenza virus genetic diversity in some gene segments as all other mammalian and avian species combined. The crystal structures of the hemagglutinin and neuraminidase proteins indicate that sialic acid is not a receptor for virus attachment nor a substrate for release, suggesting a novel mechanism of influenza A virus attachment and activation of membrane fusion for entry into host cells. In summary, our findings indicate that bats constitute a potentially important reservoir for influenza viruses.

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          Most cited references 23

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          Receptor binding and membrane fusion in virus entry: the influenza hemagglutinin.

          Hemagglutinin (HA) is the receptor-binding and membrane fusion glycoprotein of influenza virus and the target for infectivity-neutralizing antibodies. The structures of three conformations of the ectodomain of the 1968 Hong Kong influenza virus HA have been determined by X-ray crystallography: the single-chain precursor, HA0; the metastable neutral-pH conformation found on virus, and the fusion pH-induced conformation. These structures provide a framework for designing and interpreting the results of experiments on the activity of HA in receptor binding, the generation of emerging and reemerging epidemics, and membrane fusion during viral entry. Structures of HA in complex with sialic acid receptor analogs, together with binding experiments, provide details of these low-affinity interactions in terms of the sialic acid substituents recognized and the HA residues involved in recognition. Neutralizing antibody-binding sites surround the receptor-binding pocket on the membrane-distal surface of HA, and the structures of the complexes between neutralizing monoclonal Fabs and HA indicate possible neutralization mechanisms. Cleavage of the biosynthetic precursor HA0 at a prominent loop in its structure primes HA for subsequent activation of membrane fusion at endosomal pH (Figure 1). Priming involves insertion of the fusion peptide into a charged pocket in the precursor; activation requires its extrusion towards the fusion target membrane, as the N terminus of a newly formed trimeric coiled coil, and repositioning of the C-terminal membrane anchor near the fusion peptide at the same end of a rod-shaped molecule. Comparison of this new HA conformation, which has been formed for membrane fusion, with the structures determined for other virus fusion glycoproteins suggests that these molecules are all in the fusion-activated conformation and that the juxtaposition of the membrane anchor and fusion peptide, a recurring feature, is involved in the fusion mechanism. Extension of these comparisons to the soluble N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) protein complex of vesicle fusion allows a similar conclusion.
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            REFMAC5 dictionary: organization of prior chemical knowledge and guidelines for its use.

            One of the most important aspects of macromolecular structure refinement is the use of prior chemical knowledge. Bond lengths, bond angles and other chemical properties are used in restrained refinement as subsidiary conditions. This contribution describes the organization and some aspects of the use of the flexible and human/machine-readable dictionary of prior chemical knowledge used by the maximum-likelihood macromolecular-refinement program REFMAC5. The dictionary stores information about monomers which represent the constitutive building blocks of biological macromolecules (amino acids, nucleic acids and saccharides) and about numerous organic/inorganic compounds commonly found in macromolecular crystallography. It also describes the modifications the building blocks undergo as a result of chemical reactions and the links required for polymer formation. More than 2000 monomer entries, 100 modification entries and 200 link entries are currently available. Algorithms and tools for updating and adding new entries to the dictionary have also been developed and are presented here. In many cases, the REFMAC5 dictionary allows entirely automatic generation of restraints within REFMAC5 refinement runs.
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              Structure of the haemagglutinin membrane glycoprotein of influenza virus at 3 A resolution.

              The haemagglutinin glycoprotein of influenza virus is a trimer comprising two structurally distinct regions: a triple-stranded coiled-coil of alpha-helices extends 76 A from the membrane and a globular region of antiparallel beta-sheet, which contains the receptor binding site and the variable antigenic determinants, is positioned on top of this stem. Each subunit has an unusual loop-like topology, starting at the membrane, extending 135 A distally and folding back to enter the membrane.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS Pathog
                PLoS Pathog
                plos
                plospath
                PLoS Pathogens
                Public Library of Science (San Francisco, USA )
                1553-7366
                1553-7374
                October 2013
                October 2013
                10 October 2013
                : 9
                : 10
                Affiliations
                [1 ]Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
                [2 ]Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California, United States of America
                [3 ]Sydney Emerging Infections and Biosecurity Institute, School of Biological Sciences and Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia
                [4 ]Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
                [5 ]Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
                [6 ]Direccion General de Epidemiologıa, Ministerio de Salud - MINSA, Lima, Peru
                [7 ]Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California, United States of America
                [8 ]Global Alliance for Rabies Control, The Scripps Research Institute, La Jolla, California, United States of America
                [9 ]Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America
                [10 ]Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California, United States of America
                National Institutes of Health, United States of America
                Author notes

                The authors have declared that no competing interests exist.

                Conceived and designed the experiments: ST IAW JS ROD ECH JCP CER. Performed the experiments: SR JG ATG LMC AJ JZ YL YT XC MB MS CTD PJC JC HY ZG CD WY XZ RM. Analyzed the data: ST YL XZ IAW HY JS ROD LMC AJ MS ECH CTD JCP CER. Contributed reagents/materials/analysis tools: SR ATG JG ST IAW JS ROD ECH JCP CER. Wrote the paper: ST IAW JS ROD ECH JCP CER.

                Article
                PPATHOGENS-D-13-00243
                10.1371/journal.ppat.1003657
                3794996
                24130481

                This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

                Page count
                Pages: 12
                Funding
                The work was supported in part by NIH grant AI058113 (IAW and JCP), a contract from the CDC (JCP), and the Skaggs Institute for Chemical Biology. Portions of this research were conducted at SSRL, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy (DOE), Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research and by NIH, National Center for Research Resources, Biomedical Technology Program (P41RR001209), and the National Institute of General Medical Sciences. The GM/CA CAT 23-ID-D beamline has been funded in whole or in part with federal funds from National Cancer Institute (Y1-CO-1020) and NIGMS (Y1-GM-1104). Supporting institutions for SER-CAT 22-ID may be found at www.ser-cat.org/members.html. Use of the Advanced Photon Source (APS) was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Science, under contract no. DE-AC02-06CH11357 and contract no. W-31-109-Eng-38. Glycans for the arrays were provided by the Consortium for Functional Glycomics funded by NIH grants GM062116 and GM098791. This is publication 21954 from The Scripps Research Institute. ECH was supported in part by NIH grant GM080533-06. The study was supported in part by the Global Disease Detection program TSC funds in the Centers for Disease Control and Prevention, Atlanta, Georgia (ST) and in part by a collaborative Centers for Disease Control and Prevention-University of Georgia Seed Award (ST). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article

                Infectious disease & Microbiology

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