Fig. 2: Permissive mutations for NA N387K in Mos99 and SD93.

a Locations of natural mutations from Mos99 to Wy03 are shown as blue spheres on one protomer of NA that is in white cartoon representation, while the other three protomers are shown as semitransparent black surface (PDB 3TIA)²¹. Location of N387K is shown as an orange sphere. Sialic acid in the active site is shown as yellow sticks. b The compensatory effects of mutating residue 385 to Asn in different chimeric H3N2 strains were examined by a virus rescue experiment. c Locations of natural mutations from SD93 to Mos99 are shown as blue or white spheres on one protomer of NA that is in white cartoon representation, while the other three protomers are shown as semitransparent black surface (PDB 3TIA)²¹. Blue spheres represent the mutations that were included in the SD93 combinatorial mutant library. d High-throughput identification of permissive mutations for N387K in SD93. The occurrence frequency of each variant in the post-passaged mutant library is shown. A de novo mutation Y336N was emerged during passaging. Datapoints that represent mutants with Y336N are in red. The amino acid sequences of variants with >0.1% frequencies in the post-passaged mutant libraries of both biological replicates are represented by a sequence logo. e The replication fitness of different SD93 mutants was examined by a virus rescue experiments. b, e Each bar represents the mean of three independent biological replicates. Each datapoint represents one biological replicate. Virus titer was measured by TCID₅₀. The green dashed line represents the lower detection limit. Source data are provided as a Source Data file.