Gorga J C, Dong A, Manning M C, Woody R W, Caughey W S, Strominger J L
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 1989 Apr;86(7):2321-5. doi: 10.1073/pnas.86.7.2321.
We have examined the secondary structures of human class I and class II histocompatibility antigens in solution by Fourier transform infrared spectroscopy and circular dichroism in order to compare the relative amounts of alpha-helix, beta-sheet, and other structures, which are crucial elements in the comparison of the protein structures. Quantitation of infrared spectra of papain-solubilized HLA-A2, HLA-B7, and DR1 in phosphate buffer gave alpha-helix contents of 17%, 8%, and 10% and beta-sheet contents of 41%, 48%, and 53%, respectively. By circular dichroism, papain-solubilized HLA-A2, HLA-B7, and DR1 were also found to have comparable alpha-helix contents (e.g., 8%, 20%, and 17%, respectively). Circular dichroism analysis for beta-sheet gave 29% for papain-solubilized HLA-B7 and 42% for papain-solubilized DR1. The value for papain-solubilized HLA-A2 (74%) was anomalous. It is proposed that Trp-107 of HLA-A2, missing in both HLA-B7 and DR1, may be responsible for much of the anomaly. Due to the uncertainties inherent in quantitation of the amounts of secondary structures by both spectral methods, the differences in the contents of alpha-helix and beta-sheet in the three proteins are not considered significant. However, differences in the nature of the beta-sheet structures are suggested by infrared spectroscopy. These results provide physical evidence for an overall structure of class II antigens modeled on that of class I antigens.
我们通过傅里叶变换红外光谱和圆二色性研究了溶液中人类I类和II类组织相容性抗原的二级结构，以便比较α-螺旋、β-折叠和其他结构的相对含量，这些结构是比较蛋白质结构的关键要素。对木瓜蛋白酶溶解的HLA-A2、HLA-B7和DR1在磷酸盐缓冲液中的红外光谱进行定量分析，结果显示α-螺旋含量分别为17%、8%和10%，β-折叠含量分别为41%、48%和53%。通过圆二色性分析发现，木瓜蛋白酶溶解的HLA-A2、HLA-B7和DR1的α-螺旋含量也相当（例如，分别为8%、20%和17%）。对β-折叠的圆二色性分析显示，木瓜蛋白酶溶解的HLA-B7为29%，木瓜蛋白酶溶解的DR1为42%。木瓜蛋白酶溶解的HLA-A2的值（74%）异常。有人提出，HLA-B7和DR1中均缺失的HLA-A2的色氨酸-107可能是造成这种异常的主要原因。由于两种光谱方法在定量二级结构含量方面存在固有的不确定性，因此这三种蛋白质中α-螺旋和β-折叠含量的差异不被认为具有显著性。然而，红外光谱表明β-折叠结构的性质存在差异。这些结果为基于I类抗原结构构建的II类抗原的整体结构提供了物理证据。
