Enveloped animal viruses must undergo membrane fusion to deliver their genome into the host cell. We demonstrate that high pressure inactivates two membrane-enveloped viruses, influenza and Sindbis, by trapping the particles in a fusion-intermediate state. The pressure-induced conformational changes in Sindbis and influenza viruses were followed using intrinsic and extrinsic fluorescence spectroscopy, circular dichroism, and fusion, plaque, and hemagglutination assays. Influenza virus subjected to pressure exposes hydrophobic domains as determined by tryptophan fluorescence and by the binding of bis-8-anilino-1-naphthalenesulfonate, a well established marker of the fusogenic state in influenza virus. Pressure also produced an increase in the fusion activity at neutral pH as monitored by fluorescence resonance energy transfer using lipid vesicles labeled with fluorescence probes. Sindbis virus also underwent conformational changes induced by pressure similar to those in influenza virus, and the increase in fusion activity was followed by pyrene excimer fluorescence of the metabolically labeled virus particles. Overall we show that pressure elicits subtle changes in the whole structure of the enveloped viruses triggering a conformational change that is similar to the change triggered by low pH. Our data strengthen the hypothesis that the native conformation of fusion proteins is metastable, and a cycle of pressure leads to a final state, the fusion-active state, of smaller volume.Enveloped viruses utilize regulated membrane fusion to introduce their genomes in the cytoplasm of the host cell. The fusion is mediated by surface envelope proteins of the virus in response to a trigger (1, 2). Once triggered, the fusion process leads to a conformational change that promotes the interaction of a specific sequence (fusion peptide) with the target membrane and initiates membrane fusion. Membrane fusion is crucial in other biological functions such as myotube formation, fertilization, and trafficking of endocytic and exocytic vesicles within eukaryotic cells (1, 3). Many enveloped animal viruses have been studied as models for understanding the mechanism of membrane fusion. While the fusion proteins of many viruses reveal significant similarity in their putative fusogenic conformation, such as those of influenza virus (hemagglutinin HA2), 1 human immunodeficiency virus (gp41 protein), Moloney murine leukemia virus (TM protein), and Ebola virus (GP2 protein) (4), the events of membrane fusion for other virus families (e.g. Flaviviridae and Togaviridae) are beginning to be understood. Alphavirus and the flavivirus fusion proteins appear to have evolved from a common ancestor (5) and possess a similar new class of membrane fusion proteins that do not form coiledcoils (6 -8).Sindbis and influenza are enveloped viruses that first enter a cell by endocytosis and then fuse with the cellular membrane in response to acidic conditions. Sindbis virus is the prototype of the Alphavirus genus, Togaviridae family. The Alphavirus spike is...

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Membrane introduction mass spectrometry was used to study adsorption and desorption processes of a set of organic compounds (benzene, toluene, tetrahydrofuran, phenol, 1-butanol, 1-octanol, chlorobenzene, chloroform, and 1,2-dichloropropane) in aqueous solution on activated carbon. Competitive adsorption of these organic compounds on activated carbon was also suitably evaluated by MIMS. Moreover, MIMS can be used to carry out SPE (solid phase extraction) experiments in which the organic compounds are first adsorbed on activated carbon, and subsequently desorbed to water. Using the MIMS apparatus, these compounds were promptly identified and quantified.

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