Ohnishi Satoshi, Lee Andrew L, Edgell Marshall H, Shortle David
Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Biochemistry. 2004 Apr 13;43(14):4064-70. doi: 10.1021/bi049879b.
To characterize the long-range structure that persists in the unfolded form of the 70-residue protein eglin C, residual dipolar couplings (RDCs) for HN-N and HA-CA bond vectors were measured by NMR spectroscopy for both its low pH, urea denatured state and its native state. When the data sets for the two different structural states were compared, a statistically significant correlation was found, with both sets of dipolar couplings yielding a correlation coefficient of r = 0.47 to 0.51. This finding directly demonstrates that the denatured state of eglin C has a nativelike global structure, a conclusion reached indirectly for staphylococcal nuclease by combining two different types of NMR data. A simple computer simulation showed that the degree of variation in phi and psi angles that yields the RDC correlation of r = 0.5 was inversely dependent on the statistical segment length, ranging from +/-6 to +/-30 degrees at the upper limit. Stable nativelike topologies that persist on unfolding would explain the rapid refolding kinetics displayed by many proteins and might provide a natural barrier against amyloid fibril formation.
为了表征由70个残基组成的蛋白质依格林C（eglin C）在未折叠形式下依然存在的远程结构，通过核磁共振光谱法测量了其低pH值、尿素变性状态和天然状态下HN-N与HA-CA键向量的剩余偶极耦合（RDC）。当比较两种不同结构状态的数据集时，发现了具有统计学意义的相关性，两组偶极耦合的相关系数r均为0.47至0.51。这一发现直接表明依格林C的变性状态具有类似天然的整体结构，这一结论是通过结合两种不同类型的核磁共振数据间接得出的，此前葡萄球菌核酸酶也曾有过类似结论。一个简单的计算机模拟显示，产生r = 0.5的RDC相关性的φ角和ψ角的变化程度与统计片段长度成反比，上限范围为±6至±30度。在去折叠时依然存在的稳定的类似天然的拓扑结构可以解释许多蛋白质表现出的快速重折叠动力学，并且可能为防止淀粉样原纤维形成提供天然屏障。
