Gast K, Modler A J, Damaschun H, Kröber R, Lutsch G, Zirwer D, Golbik R, Damaschun G
Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Str. 10, 13125 Berlin, Germany.
Eur Biophys J. 2003 Dec;32(8):710-23. doi: 10.1007/s00249-003-0336-5. Epub 2003 Jul 26.
The dependence on environmental conditions of the assembly of barstar into amyloid fibrils was investigated starting from the nonnative, partially folded state at low pH (A-state). The kinetics of this process was monitored by CD spectroscopy and static and dynamic light scattering. The morphology of the fibrils was visualized by electron microscopy, while the existence of the typical cross-beta structure substantiated by solution X-ray scattering. At room temperature, barstar in the A-state is unable to form amyloid fibrils, instead amorphous aggregation is observed at high ionic strength. Further destabilization of the structure is required to transform the polypeptide chain into an ensemble of conformations capable of forming amyloid fibrils. At moderate ionic strength (75 mM NaCl), the onset and the rate of fibril formation can be sensitively tuned by increasing the temperature. Two types of fibrils can be detected differing in their morphology, length distribution and characteristic far UV CD spectrum. The formation of the different types depends on the particular environmental conditions. The sequence of conversion: A-state-->fibril type I-->fibril type II appears to be irreversible. The transition into fibrils is most effective when the protein chain fulfills particular requirements concerning secondary structure, structural flexibility and tendency to cluster.
从低pH值下的非天然部分折叠状态（A态）开始，研究了巴氏星状菌素组装成淀粉样纤维对环境条件的依赖性。通过圆二色光谱法以及静态和动态光散射监测该过程的动力学。通过电子显微镜观察纤维的形态，同时通过溶液X射线散射证实典型交叉β结构的存在。在室温下，A态的巴氏星状菌素无法形成淀粉样纤维，而是在高离子强度下观察到无定形聚集。需要进一步使结构不稳定，才能将多肽链转化为能够形成淀粉样纤维的一系列构象。在中等离子强度（75 mM NaCl）下，通过升高温度可以灵敏地调节纤维形成的起始和速率。可以检测到两种形态、长度分布和特征远紫外圆二色光谱不同的纤维。不同类型的形成取决于特定的环境条件。转化顺序：A态→I型纤维→II型纤维似乎是不可逆的。当蛋白质链满足有关二级结构、结构灵活性和聚集倾向的特定要求时，向纤维的转变最为有效。
