Yoden S, Kida H, Kuwabara M, Yanagawa R, Webster R G
Virus Res. 1986 May;4(3):251-61. doi: 10.1016/0168-1702(86)90004-3.
To study the conformational changes in the hemagglutinin (HA) molecule of A/seal/Mass/1/80 (H7N7) (Seal) influenza virus at low pH, a spin-labeling method was used. This method also permits study of antibody interaction with the HA. A synthetic nitroxide compound was used for spin-labeling of tyrosine residues of the isolated HA molecule. Electron spin resonance (ESR) spectra of the spin-labeled HA at various pH values indicated that a conformational transition occurred under acidic conditions, and around pH 5.8 the HA molecule has maximal flexibility. Since virus-induced hemolysis occurs optimally at pH 5.8-5.9, the HA molecule in the maximally flexible conformation is considered to mediate membrane fusion. The ESR spectra of the antibody-bound HA at various pH values revealed that monoclonal antibodies to different regions on the molecule may inhibit the conformational change by different modes. One antibody inhibited the changes in the HA that resulted in flexibility, while the other did not. These results support the assumption that monoclonal antibodies, which failed to inhibit hemagglutination of the virus yet neutralized viral infectivity, inhibited the fusion step in the viral replication process by interfering with a low pH-induced conformational change in the HA molecule (Kida, H., Webster, R.G. and Yanagawa, R. (1983) Arch. Virol. 76, 91-99).
为研究A/海豹/马萨诸塞/1/80（H7N7）（海豹型）流感病毒血凝素（HA）分子在低pH值下的构象变化，采用了自旋标记法。该方法还可用于研究抗体与HA的相互作用。一种合成的氮氧化物化合物用于对分离出的HA分子的酪氨酸残基进行自旋标记。不同pH值下自旋标记HA的电子自旋共振（ESR）光谱表明，在酸性条件下发生了构象转变，在pH 5.8左右HA分子具有最大的灵活性。由于病毒诱导的溶血在pH 5.8 - 5.9时最佳发生，因此处于最大灵活构象的HA分子被认为介导膜融合。不同pH值下抗体结合HA的ESR光谱显示，针对分子不同区域的单克隆抗体可能通过不同方式抑制构象变化。一种抗体抑制了导致灵活性的HA变化，而另一种则没有。这些结果支持了这样的假设，即未能抑制病毒血凝但能中和病毒感染性的单克隆抗体，通过干扰低pH诱导的HA分子构象变化，抑制了病毒复制过程中的融合步骤（木田浩、韦伯斯特·R·G、柳川润（1983年）《病毒学文献》76卷，91 - 99页）。
