Collapse and search dynamics of apomyoglobin folding revealed by submillisecond observations of α-helical content and compactness
Collapse and search dynamics of apomyoglobin folding revealed by submillisecond observations of α-helical content and compactness
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DOI：
10.1073/pnas.0305376101
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发表时间：
2004-02-03
影响因子：
11.1
通讯作者：
Fujisawa, T
中科院分区：
文献类型：
--
作者：
Uzawa, T;Akiyama, S;Fujisawa, T
蛋白质折叠动力学在二级和三级结构方面的表征对于阐明导致特定折叠结构的蛋白质内相互作用的特征非常重要。脱肌红蛋白 (apoMb) 在天然状态下拥有 7 个螺旋，分别为 A-E、G 和 H，具有由 A、G 和 H 螺旋组成的折叠中间体，其在亚毫秒时间域中的形成尚未明确表征。在本研究中，我们使用快速混合装置结合圆二色性和小角X射线散射，分别观察apoMb的螺旋含量（f（H））和回转半径（R-g）的亚毫秒折叠动力学。 pH 值跃升至 6.0 时，apoMb 在 pH 值 2.2 时从酸解折叠状态开始折叠。在 pH 跳跃后 300Its 内观察到显着的崩溃，相当于 R-g 从展开到天然构象的总体变化的大约 50%。塌陷的中间体的 f(H) 为 33%，呈球状，占所有原子的 80% 以上。随后，检测到逐步螺旋形成，这被解释为与正确三级接触的构象搜索有关。 apoMb 的折叠动力学特征表明初始折叠事件的重要性，这有助于随后的构象搜索和导致天然结构的螺旋形成。
The characterization of protein folding dynamics in terms of secondary and tertiary structures is important in elucidating the features of intraprotein interactions that lead to specific folded structures. Apomyoglobin (apoMb), possessing seven helices termed A-E, G, and H in the native state, has a folding intermediate composed of the A, G, and H helices, whose formation in the submillisecond time domain has not been clearly characterized. In this study, we used a rapid-mixing device combined with circular dichroism and small-angle x-ray scattering to observe the submillisecond folding dynamics of apoMb in terms of helical content (f(H)) and radius of gyration (R-g), respectively. The folding of apoMb from the acid-unfolded state at pH 2.2 was initiated by a pH jump to 6.0. A significant collapse, corresponding to approximate to50% of the overall change in R-g from the unfolded to native conformation, was observed within 300 Its after the pH jump. The collapsed intermediate has a f(H) of 33% and a globular shape that involves >80% of all its atoms. Subsequently, a stepwise helix formation was detected, which was interpreted to be associated with a conformational search for the correct tertiary contacts. The characterized folding dynamics of apoMb indicates the importance of the initial collapse event, which is suggested to facilitate the subsequent conformational search and the helix formation leading to the native structure.