The analysis of the restriction of amino acid substitution on the hemagglutinin molecule of influenza A virus

点击翻译按钮获取中文摘要

In order to clarify the effect of accumulation of amino acid substitutions on the hemadsorption character of influenza AH3 hemagglutinin (HA) protein, we introduced single-point amino acid changes into the HA1 domain of the HA protein of influenza viruses isolated in 1968 (A/Aichi/2/68) and 1997 (A/Sydney/5/97) using PCR random mutation or site-directed mutagenesis. These substitutions were classified as positive or negative according to their effect on hemadsorption activity. The rate of positive substitutions was about 50% in both strains. Out of 44 amino acid changes that were identical in the two strains with regard to both the substituted amino acids and their positions in the HA1 domain, 22% of changes that were positive in A/Aichi/2/68 were negative in A/Sydney/5/97 and 27% of changes that were negative in A/Aichi/2/68 were positive in A/Sydney/5/97. A similar discordance rate was also seen with the antigenic sites. These results suggest that the accumulation of amino acid substitutions in the HA protein during evolution promoted irreversible structural changes and therefore antigenic changes in H3HA protein may not be limited. On the other hand, from the analysis of amino acids participating in mainstream amino acid change, each antigenic site could be further divided into smaller sites. The amino acid substitutions in the gaps between these smaller sites resulted in mostly hemadsorption-negative changes. These gap positions may play an important role in maintaining the function of the HA protein, and therefore, amino acid changes are restricted at these locations