Wharton S A, Ruigrok R W, Martin S R, Skehel J J, Bayley P M, Weis W, Wiley D C
Division of Virology, National Institute for Medical Research, London, Great Britain.
J Biol Chem. 1988 Mar 25;263(9):4474-80.
Circular dichroism and tryptophan fluorescence spectroscopy have been used to investigate the structures of the influenza virus membrane glycoprotein hemagglutinin, acid-treated hemagglutinin, and fragments of hemagglutinin derived by proteolysis. The conformational change in hemagglutinin which occurs at the pH of membrane fusion (pH 5-6) was associated with a significant change of the environment of tyrosine residues, a change in the environment of tryptophan residues, but no changes in secondary structure. Tryptic digestion of the hemagglutinin in its low pH conformation which releases one of the subunit polypeptides (HA1) caused minimal changes in tyrosine and tryptophan environments but a small secondary structural change in HA1. The secondary structure of the remainder of the molecule (HA2) was very similar to that predicted from the known x-ray crystallographic structure of the native molecule. However, fluorescence spectroscopy indicated a tertiary change in structure in the coiled coil of alpha-helices which form the fibrous central stem of the molecule. These results are consistent with a conformational change required for membrane fusion which involves a decrease of HA1/HA1, HA1/HA2 interactions and changes in tertiary structure not accompanied by changes in secondary structure.
圆二色光谱和色氨酸荧光光谱已被用于研究流感病毒膜糖蛋白血凝素、酸处理血凝素以及通过蛋白水解得到的血凝素片段的结构。在膜融合pH值（pH 5 - 6）时血凝素发生的构象变化与酪氨酸残基环境的显著变化、色氨酸残基环境的变化相关，但二级结构没有变化。在低pH构象下对血凝素进行胰蛋白酶消化，释放出一个亚基多肽（HA1），这导致酪氨酸和色氨酸环境的变化最小，但HA1有一个小的二级结构变化。分子其余部分（HA2）的二级结构与根据天然分子已知的X射线晶体结构预测的结构非常相似。然而，荧光光谱表明，形成分子纤维状中央茎的α - 螺旋卷曲螺旋结构发生了三级结构变化。这些结果与膜融合所需的构象变化一致，这种变化涉及HA1/HA1、HA1/HA2相互作用的减少以及三级结构的变化，而二级结构没有变化。
