Oligomeric organization and strain-specific proteolytic modification of the virion M2 protein of influenza A H1N1 viruses.

The M2 protein of influenza A H1N1 strains PR8, WS, and WSN is present in homooligomeric forms in virions grown in the allantoic cavity of embryonated eggs. The bulk of the virion M2 is detected as tetramers and dimers. The oligomeric forms of PR8 virions differ from those of WS and WSN not only in apparent molecular weight (MW) but also in that they seem to be composed of two types of monomers differing in MW by approximately 1.5 kDa. Evidence from monoclonal antibody binding (or lack of it) and from in vitro trypsin digestion suggests that, in ovo, the external NH2 region of some PR8 M2 monomers is proteolytically trimmed, resulting in heterogeneous oligomers composed of cleaved and uncleaved monomers in different proportions.