Amino acid changes in the hemagglutinin and matrix proteins of influenza A(H2) viruses adapted to mice

Mouse-adapted (MA) variants of human and avian influenza A (H2) viruses wer e generated and characterized with respect to acquisition of virulence in m ice. From the nucleotide sequence the amino acid sequence was deduced. The HA 1 subunit of the hemagglutinin (HA) contained three amino acid substitut ions in the A/black duck/New Jersey/1580/78-MA variant (Glu216-->Asp, Lys30 7-->Arg, and Thr318-->Ile) and two substitutions in the A/JapanxBellamy/57- MA variant (Lys25-->Thr and Ser203-->Phe). In the hll protein, there were t wo substitutions in the A/black duck/New Jersey/1580/78-MA variant (Asn30-- >Asp and Gln214-->His) and a single substitution in the A/JapanxBellamy/57- MA variant (Met179-->Lys). The M2 protein amino acid sequences of the paren tal virus and the MA variants differed by a single identical mutation (Asn9 3-->Ser), The localization and atomic distances of the observed mutations o n the three-dimensional (3D) structure of the I-IA protein were analyzed fo r influenza H2 viruses. The obtained results were similar to those publishe d earlier on H1, H3 and H5 subtypes. The amino acid changes in the HA prote in could be divided into two groups, In one group the substitutions were si tuated at the top of the molecule, while in the other group they were clust ered in the stem area at the interface region between three HA monomers. Th e analysis revealed that the substitutions observed in the MA variants prob ably increase the flexibility of the HA molecule and/or weaken the interact ions between monomers or subunits in the HA trimer. The relationships of th e observed amino acid changes in the IIA and M proteins to the biological p roperties of the respective viruses and possible mechanisms involved in the acquisition of viral virulence are discussed.