Safar J, Roller P P, Ruben G C, Gajdusek D C, Gibbs C J
Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
Biopolymers. 1993 Sep;33(9):1461-76. doi: 10.1002/bip.360330915.
The solid state secondary structure of myoglobin, RNase A, concanavalin A (Con A), poly(L-lysine), and two linear heterooligomeric peptides were examined by both far-uv CD spectroscopy1 and by ir spectroscopy. The proteins associated from water solution on glass and mica surfaces into noncrystalline, amorphous films, as judged by transmission electron microscopy of carbon-platinum replicas of surface and cross-fractured layer. The association into the solid state induced insignificant changes in the amide CD spectra of all alpha-helical myoglobin, decreased the molar ellipticity of the alpha/beta RNase A, and increased the molar ellipticity of all-beta Con A with no change in the positions of the bands' maxima. High-temperature exposure of the films induced permanent changes in the conformation of all proteins, resulting in less alpha-helix and more beta-sheet structure. The results suggest that the protein alpha-helices are less stable in films and that the secondary structure may rearrange into beta-sheets at high temperature. Two heterooligomeric peptides and poly(L-lysine), all in solution at neutral pH with "random coil" conformation, formed films with variable degrees of their secondary structure in beta-sheets or beta-turns. The result corresponded to the protein-derived Chou-Fasman amino acid propensities, and depended on both temperature and solvent used. The ir and CD spectra correlations of the peptides in the solid state indicate that the CD spectrum of a "random" structure in films differs from random coil in solution. Formic acid treatment transformed the secondary structure of the protein and peptide films into a stable alpha-helix or beta-sheet conformations. The results indicate that the proteins aggregate into a noncrystalline, glass-like state with preserved secondary structure. The solid state secondary structure may undergo further irreversible transformations induced by heat or solvent.
通过远紫外圆二色光谱法和红外光谱法对肌红蛋白、核糖核酸酶A、伴刀豆球蛋白A（Con A）、聚（L-赖氨酸）以及两种线性杂合寡聚肽的固态二级结构进行了研究。从水溶液中吸附在玻璃和云母表面的蛋白质形成了非晶态、无定形的膜，这是通过对表面和交叉断裂层的碳铂复制品进行透射电子显微镜观察判断得出的。形成固态时，所有α-螺旋结构的肌红蛋白的酰胺圆二色光谱变化不显著，α/β结构的核糖核酸酶A的摩尔椭圆率降低，全β结构的伴刀豆球蛋白A的摩尔椭圆率增加，且谱带最大值位置不变。薄膜在高温下暴露会导致所有蛋白质的构象发生永久性变化，使得α-螺旋结构减少，β-折叠结构增多。结果表明，蛋白质的α-螺旋在薄膜中稳定性较差，并且二级结构在高温下可能会重排为β-折叠结构。两种杂合寡聚肽和聚（L-赖氨酸）在中性pH的溶液中均呈“无规卷曲”构象，形成的薄膜具有不同程度的β-折叠或β-转角二级结构。结果与源自蛋白质的周-法斯曼氨基酸倾向相符，并且取决于温度和所用溶剂。固态下肽的红外光谱和圆二色光谱相关性表明，薄膜中“无规”结构的圆二色光谱与溶液中的无规卷曲不同。甲酸处理可将蛋白质和肽薄膜的二级结构转变为稳定的α-螺旋或β-折叠构象。结果表明，蛋白质聚集形成具有保留二级结构的非晶态、类似玻璃的状态。固态二级结构可能会因加热或溶剂作用而发生进一步的不可逆转变。
