Hadden J M, Bloemendal M, Haris P I, van Stokkum I H, Chapman D, Srai S K
Department of Protein and Molecular Biology, Royal Free Hospital School of Medicine, London, UK.
FEBS Lett. 1994 Aug 22;350(2-3):235-9. doi: 10.1016/0014-5793(94)00774-8.
Fourier transform infrared spectroscopy has been used to study the solution structure and thermal stability of the extracellular fragment of human transferrin receptor (tfRt) at extracellular and endosomal pH. At extracellular pH tfRt is composed of 56% alpha-helix, 19% beta-sheet and 14% turns. Upon acidification to endosomal pH the alpha-helical content of the protein is reduced and the beta-sheet content increased by nearly 10%. At extracellular pH, the midpoint temperature of thermal denaturation (Tm) for the loss of secondary and tertiary structure, and the formation of aggregated structures, is 71 degrees C. At endosomal pH this temperature is reduced by approximately 15 degrees C. The apparent entropies of thermal denaturation indicate that the native structure of tfRt at endosomal pH is far more flexible than at extracellular pH.
傅里叶变换红外光谱已被用于研究人转铁蛋白受体（tfRt）细胞外片段在细胞外和内体pH值下的溶液结构和热稳定性。在细胞外pH值下，tfRt由56%的α-螺旋、19%的β-折叠和14%的转角组成。酸化至内体pH值后，蛋白质的α-螺旋含量降低，β-折叠含量增加近10%。在细胞外pH值下，二级和三级结构丧失以及聚集结构形成的热变性中点温度（Tm）为71℃。在内体pH值下，该温度降低约15℃。热变性的表观熵表明，tfRt在内体pH值下的天然结构比在细胞外pH值下更加灵活。
