Matrix protein 2 forms a proton-selective channel that required for
the release of the viral genome during entry. After binding
receptors on the host cell surface, the virus enters the cell by
endocytosis, which acidifies the endosome. The low pH causes an
activation of the channels, which then allow the influx of protons
into the viral particle. The acidity weakens the association of
matrix protein 1 with the nucleoprotein, uncovering the nuclear
localization sites, and facilitates viral uncoating. With the
nuclear localization sites uncovered, the genome can migrate to the
host nucleus. The M2 protein may also regulate and maintain the
high pH in the lumen of the trans-Golgi network. For
hemagglutinin (HA) proteins with polybasic cleavage sites, M2
activity could protect HA proteins from premature conformational
changes in the trans-Golgi network
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