title: Intravirion cohesion of matrix protein M1 with ribonucleocapsid is a prerequisite of influenza virus infectivity.
abstract: Influenza virus has two major structural modules, an external lipid envelope and an internal ribonucleocapsid containing the genomic RNA in the form of the ribonucleoprotein (RNP) complex, both of which are interlinked by the matrix protein M1. Here we studied M1-RNP cohesion within virus exposed to acidic pH in vitro. The effect of acidification was dependent on the cleavage of the surface glycoprotein HA. Acidic pH caused a loss of intravirion RNP-M1 cohesion and activated RNP polymerase activity in virus with cleaved HA (HA1/2) but not in the uncleaved (HA0) virus. The in vitro acidified HA1/2 virus rapidly lost infectivity whereas the HA0 one retained infectivity, following activation by trypsin, suggesting that premature activation and release of the RNP is detrimental to viral infectivity. Rimantadine, an inhibitor of the M2 ion channel, was found to protect the HA1/2 virus interior against acidic disintegration, confirming that M2-dependent proton translocation is essential for the intravirion RNP release and suggesting that the M2 ion channel is only active in virions with cleaved HA. Acidic treatment of both HA0 and HA1/2 influenza viruses induces formation of spikeless bleb-like protrusion of ~ 25 nm in diameter on the surface of the virion, though only the HA1/2 virus was permeable to protons and permitted RNP release. It is likely that this bleb corresponds to the M2-enriched and M1-depleted focus arising from pinching off of the virus during the completion of budding. Cooperatively, the data suggest that the influenza virus has an asymmetric structure where the M1-mediated organization of the RNP inside the virion is a prerequisite for infectious entry into target cell.
authors.affiliation: D.I. Ivanovsky Institute of Virology, Moscow 123098, Russia. Electronic address: zhirnov@inbox.ru.
authors.forename: O P
authors.initials: OP
authors.lastname: Zhirnov
authors.affiliation: D.I. Ivanovsky Institute of Virology, Moscow 123098, Russia.
authors.forename: A A
authors.initials: AA
authors.lastname: Manykin
authors.affiliation: School of Biosciences, University of Kent, Canterbury CT27NJ, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: Rossman
authors.affiliation: Institute of Virology, Philipps University, Marburg 35037, Germany.
authors.forename: H D
authors.initials: HD
authors.lastname: Klenk
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002642:Chick Embryo; D004285:Dogs; D015870:Gene Expression; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D061985:Madin Darby Canine Kidney Cells; D019251:Nucleocapsid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011522:Protons; D012299:Rimantadine / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014763:Viral Matrix Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014771:Virion / Q000187:drug effects / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D014774:Virulence; D053586:Virus Internalization / Q000187:drug effects; D000086082:Viroporin Proteins
chemical_list: D000998:Antiviral Agents; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D011522:Protons; D012299:Rimantadine; D014357:Trypsin; D014763:Viral Matrix Proteins; C488936:M1 protein, Influenza A virus; C488937:M2 protein, Influenza A virus; D000086082:Viroporin Proteins; C483468:hemagglutinin, human influenza A virus
keywords: Asymmetric structure; Cleavage HA; Influenza virus; Ion channel M2; Protein M1; Virus entry