Restriction of amino acid changes on the H3 hemagglutinin protein of influenza A virus: comparison of amino acid changes observed in nature and in vitro

Abstract

We introduced 146 single-point amino acid changes into the HA1 protein of the A/Aichi/2/68 (A/Aichi/68)(H3N2) strain. These changes were classified as positive (do not abrogate hemadsorption) or negative according to their effect on hemadsorption activity. The percentage of positive was 47%. Out of 26 amino acid positions that were changed in vitro and matched with those of mainstream amino acid changes of the HA1 polypeptide, 25 were positive. From the analysis of amino acids participating in the mainstream amino acid changes, each antigenic site was further divided into smaller parts. The amino acid substitutions in the gaps between the smaller parts of the antigenic sites mostly resulted in hemadsorption-negative changes.