Abnormal Morphological Vesicles in Influenza A Virus Exposed to Acid pH

Ultrastructural Aspects of Photodynamic Inactivation of Highly Pathogenic Avian H5N8 Influenza Virus

Ultrastructural studies revealing morphological differences between intact and photodynamically inactivated virions can point to inactivation mechanisms and molecular targets. Using influenza as a model system, we show that photodynamic virus inactivation is possible without total virion destruction. Indeed, irradiation with a relatively low concentration of the photosensitizer (octacationic octakis(cholinyl) zinc phthalocyanine) inactivated viral particles (the virus titer was determined in Madin Darby Canine Kidney (MDCK) cells) but did not destroy them. Transmission electron microscopy (TEM) revealed that virion membranes kept structural integrity but lost their surface glycoproteins. Such structures are known as “bald” virions, which were first described as a result of protease treatment. At a higher photosensitizer concentration, the lipid membranes were also destroyed. Therefore, photodynamic inactivation of influenza virus initially results from surface protein removal, followed by complete virion destruction. This study suggests that photodynamic treatment can be used to manufacture “bald” virions for experimental purposes. Photodynamic inactivation is based on the production of reactive oxygen species which attack and destroy biomolecules. Thus, the results of this study can potentially apply to other enveloped viruses and sources of singlet oxygen.

RNA structure interactions and ribonucleoprotein processes of the influenza A virus

In one more years, we will ‘celebrate’ an exact centenary of the Spanish flu pandemic. With the rapid evolution of the influenza virus, the possibility of novel pandemic remains ever a concern. This review covers our current knowledge of the influenza A virus: on the role of RNA in translation, replication, what is known of the expressed proteins and the protein products generated from alternative splicing, and on the role of base pairing in RNA structure. We highlight the main events associated with viral entry into the cell, the transcription and replication process, an export of the viral genetic material from the nucleus and the final release of the virus. We discuss the observed potential roles of RNA secondary structure (the RNA base-pairing arrangement) and RNA/RNA interactions in this scheme.

Asymmetric structure of the influenza A virus and novel function of the matrix protein M1

Influenza virus is an enveloped virus. It comprises two major modules: external lipoprotein envelope and internal ribonucleoprotein (RNP) containing the genomic negative-strand RNA. Lipoprotein envelope contains four vital proteins: hemagglutinin (HA), neuraminidase (NA), transmembrane ionic channel M2, and minor amounts of nuclear export protein NEP. RNP contains RNA and four polypeptides: major nucleocapsid protein NP and three polymerase subunits PB1, PB2, PA. Both modules are linked with each other by matrix M1 maintaining the virus integrity. According to the structural function, NP and M1 are predominant in virus particle in the amounts of 1000 and 3000 molecules, respectively. In addition to the structural function, M1 plays a role in regulation of intracellular and nuclear migration of viral RNP and virus assembly, referred as budding process, at the plasma membrane in infected cells. The bipolar structure of the influenza virus characterized by asymmetric location of RNP and nonregular distribution of M1 and M2 inside the virion is reviewed. The role of M1 in maintaining the asymmetric structure of the virus particle and regulation of RNP transport inside virus particle is considered. First experimental data confirming (i) intravirion RNP transport and its outside exit directed by the M1 and (ii) the importance of this process in virus uncoating and initiation of infection in target cell are discussed. A novel class of antiviral agents activating ATP-ase of the early endosome compartment in the target cell is discussed.