A molecular mechanism for the low pH stability of sialidase activity of influenza A virus N2 neuraminidases

Abstract

Four human pandemic influenza A virus strains isolated in 1957 and 1968, but not most of the epidemic strains isolated after 1968, possess sialidase activity under low pH conditions. Here we used cell-expressed neuraminidases (NAs) to determine the region of the N2 NA that is associated with low pH stability of sialidase activity. We found that consensus among amino acid regions responsible for low pH stability did not exist in pandemic NAs, but that two amino acid substitutions in the low-pH, stable A/Hong Kong/1/68 (H3N2) NA and a single substitution in the low pH, unstable A/Texas/68 (H2N2) NA resulted in significant change in low pH stability.