TABLE 1.

Receptor-binding characteristics and sensitivities to oseltamivir carboxylate of HA variants of A/Memphis/14/96 (H1N1)

VariantAmino acid substitution in the HAaBinding affinityc, Kass (ml/U)Sensitivity to oseltamivir carboxylate, IC90 (μM)d
2,6-Fetuin-HRP2,3-Fetuin-HRP24 h48 h
M3.3 ± 0.100.046 ± 0.0210.11.0
M1E156K4.9 ± 0.580.70 ± 0.30NDe0.01
EN129Kb4.8 ± 0.600.48 ± 0.200.01NTf
E1Q226R0.09 ± 0.020.85 ± 0.31>100>100
  • a With respect to HA sequence of variant M. H3 numbering system.

  • b The mutation destroys a glycosylation sequon in the HA.

  • c Affinity of virus binding to HRP-labeled resialylated fetuins containing either 6-linked or 3-linked sialic acid moieties. The higher values of association constants (Kass) reflect higher affinities.

  • d Focus reduction assay in MDCK-SIATI cells was performed on two different occasions, with infection times of 24 and 48 h, respectively (see the text). IC90, 90% inhibitory concentration.

  • e ND, not determined. IC90 of MI variant could not be determined due to a poor virus spread 24 h postinfection.

  • f NT, not tested.