Hefei National Laboratory for Physical Sciences at the Microscale & School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China.
Department of Biological Sciences, National University of Singapore, Singapore.
Biophys J. 2019 Jul 23;117(2):239-246. doi: 10.1016/j.bpj.2019.06.012. Epub 2019 Jun 20.
Structural dynamics of fatty acid binding proteins (FABPs), which accommodate poorly soluble ligands in the internalized binding cavities, are intimately related to their function. Recently, local unfolding of the α-helical cap in a variant of human intestinal FABP (IFABP) has been shown to correlate with the kinetics of ligand association, shedding light on the nature of the critical conformational reorganization. Yet, the physical origin and mechanism of the functionally relevant transient unfolding remain elusive. Here, we investigate the intrinsic structural instability of the second helix (αII) of IFABP in comparison with other segments of the protein using hydrogen-exchange NMR spectroscopy, microsecond molecular dynamics simulations, and enhanced sampling techniques. Although tertiary interactions positively contribute to the stability of helices in IFABP, the intrinsic unfolding tendency of αII is encoded in its primary sequence and can be described by the Lifson-Roig theory in the absence of tertiary interactions. The unfolding pathway of αII in intact proteins involves an on-pathway intermediate state that is characterized with the fraying of the last helical turn, captured by independent enhanced sampling methods. The simulations in this work, combined with hydrogen-exchange NMR data, provide new, to our knowledge, atomistic insights into the functional local unfolding of FABPs.
脂肪酸结合蛋白（FABP）的结构动力学与其功能密切相关，这些蛋白可以在内部结合腔中容纳溶解性较差的配体。最近，已经证明人类肠道 FABP（IFABP）变体中α-螺旋帽的局部展开与配体结合的动力学相关，这揭示了关键构象重排的本质。然而，与功能相关的瞬时展开的物理起源和机制仍然难以捉摸。在这里，我们使用氢氘交换 NMR 光谱、微秒分子动力学模拟和增强采样技术，研究了 IFABP 中第二螺旋（αII）与蛋白质其他片段相比的固有结构不稳定性。尽管三级相互作用对 IFABP 中螺旋的稳定性有积极贡献，但αII 的固有展开趋势编码在其一级序列中，并且在没有三级相互作用的情况下可以用 Lifson-Roig 理论来描述。完整蛋白质中αII 的展开途径涉及到一个途径中间状态，其特征是最后一个螺旋圈的磨损，这是通过独立的增强采样方法捕获的。这项工作中的模拟与氢氘交换 NMR 数据相结合，为我们提供了新的、据我们所知的 FABP 功能局部展开的原子水平见解。
