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

为了阐明氨基酸取代的积累对流感病毒AH 3血凝素（HA）蛋白的血吸附特性的影响，我们采用PCR随机突变或定点突变的方法，在1968年（A/Aichi/2/68）和1997年（A/Sydney/5/97）分离的流感病毒HA蛋白的HA 1结构域中引入单点氨基酸改变。根据对红细胞吸附活性的影响，将这些取代分为阳性或阴性。两个菌株的正置换率均在50%左右。在两个菌株中就取代的氨基酸及其在HA 1结构域中的位置而言相同的44个氨基酸变化中，在A/Aichi/2/68中为阳性的变化中有22%在A/Sydney/5/97中为阴性，在A/Aichi/2/68中为阴性的变化中有27%在A/Sydney/5/97中为阳性。在抗原位点也观察到类似的不一致率。这些结果表明，HA蛋白在进化过程中氨基酸取代的积累促进了不可逆的结构变化，因此H3 HA蛋白的抗原性变化可能不受限制。另一方面，从参与主流氨基酸变化的氨基酸分析，每个抗原位点可以进一步划分为更小的位点。在这些较小的网站之间的差距的氨基酸取代主要导致血吸附负的变化。这些缺口位置可能在维持HA蛋白的功能方面发挥重要作用，因此，氨基酸变化在这些位置受到限制

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