Influenza A Viral Particle With A Fusion Competent HA2 Influenza A Viral Particle Docked At The Endocytic Vesicle Membrane Fusion of the influenza virion HA2 protein transmembrane domain to the host cell endosome membrane GENE ONTOLOGYGO:0019064 Pubmed11208147 Reactome Database ID Release 43168312 Reactome, http://www.reactome.org ReactomeREACT_6180 The fusion peptide of its HA2 subunit interacts with the endosome membrane. The transmembrane domain of the HA2 is inserted into the viral membrane and the fusion peptide is inserted into the endosomal membrane. In the acidic pH structure of HA the two ends of the HA complex are in juxtaposition.