Amino acid sequence changes in antigenic variants of type A influenza virus N2 neuraminidase

Abstract

Pronase-released neuraminidase heads from six strains of influenza type A virus (of the H2N2 and H3N2 subtypes) isolated between 1957 and 1975 were examined for changes in amino acid sequence. In 469 residues 19 changes which occurred during this period were located. Two regions of the neuraminidase molecule were not examined, residues 188–210 which were insoluble, and residues 1–73 (or 76) which formed part of the stalk of the neuraminidase and were removed during Pronase digestion. Neuraminidase heads from seven variants of A/Tokyo/3/67 virus, selected with different monoclonal antibodies to the neuraminidase were also examined for sequence changes. In four of these, a single sequence change at position 344 of arginine to isoleucine was found, in another variant an asparagine residue at position 221 changed to histidine and in another the lysine at position 368 changed to glutamic acid. This last change also occurred in the field strains isolated in 1972 and 1975. In the seventh monoclonal variant the change could not be found and may be in the insoluble region. Some of these sequence changes were clustered into two highly variable regions in the neuraminidase comprising residues 344–347 and 367–370, suggesting that these regions may be involved in antigenic sites on the neuraminidase molecule. An antigenic map of N2 neuraminidase [R. G. Webster, V. S. Hinshaw, and W. G. Laver, Virology 117, 93–104 (1982)] suggested three or four nonoverlapping antigenic areas and the variants with changes at residues 344 and 368 were grouped in one of these antigenic regions. Sequence changes in the region of 344–347 were also associated with changes in the stability of the neuraminidase. The four monoclonal variants with a sequence change of Arg (344) to Ile possessed neuraminidase molecules which were destroyed by Pronase at 37° (but not at 20°) whereas wild-type neuraminidase was stable during digestion at 37°.