A A212T Substitution in Hemagglutinin Impacts on the Rescue of Influenza A(H1N1)/B Chimeric Live-Attenuated Vaccine Candidate

The influenza virus, a viral respiratory pathogen, causes major morbidity and mortality worldwide. In this study, we compared and analyzed the effectiveness of the rescued two chimeric H1N1 vaccine strains rA/B-California/04/2009 and rA/B-California/07/2009, respectively, which expressed the hemagglutinin of A/California/07/2009 or A/California/04/2009 based on an influenza B virus master donor. The rA/B-California/07/2009 strain was rescued successfully. However, the rA/B-California/04/2009, which expressed the HA of A/California/07/2009 could hardly be generated. In substitution for alanine at residue 212 in the chimeric HA protein of rA/B-California/04/2009 virus, threonine was identified as a deleterious change. The free Gibbs energy change of mutating residue 212 reflected that threonine in site 212 caused a reduction in the stability of rA/B-California HAs. Additionally, with the analysis of binding free energy data and RMSD values of receptor analogs and two chimeric HAs, substitution 212T also conferred decreased receptor-binding avidity. These results suggested that the substitution A212T may enhance the stability and binding affinity of the chimeric H1N1 vaccine strains. This finding may help to design a live-attenuated influenza vaccine with more efficacy.