Functional stability of water wire-carbonyl interactions in an ion channel
Functional stability of water wire-carbonyl interactions in an ion channel
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DOI：
10.1073/pnas.2001083117
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发表时间：
2020-06-02
影响因子：
11.1
通讯作者：
Cross, Timothy A.
中科院分区：
文献类型：
--
作者：
Paulino, Joana;Yi, Myunggi;Cross, Timothy A.
水导线对于许多膜蛋白的功能至关重要，例如在传导水、质子和其他离子的通道中。在此，在对称环境条件下的液晶脂质双层中，包含水线的八个沃茨和衬于反平行二聚短杆菌肽A通道的26个羰基氧的子集之间的选择性氢键相互作用通过35.2 T（或对于H-1为1，500 MHz）下的O-17 NMR光谱和计算研究来表征。虽然骨架N-15光谱清楚地表明两个亚基之间的结构对称性，单网站O-17标记的孔内衬羰基报告两个共振，这意味着在二聚体对称性的选择性相互作用所造成的破坏与水线。O-17位移记录了选择性水与羰基氧的氢键合，其在毫秒时间尺度上是稳定的。这样的相互作用支持的密度泛函理论计算的快照从分子动力学模拟。水在孔隙中的氢键仅限于三个同时相互作用，不像散装水环境。水线取向及其电偶极子的稳定性导致在孔的两端结合的K+离子的相反电荷-偶极子相互作用，从而提供了一个简单的解释，两个结合位点之间的K+亲和力的相似的20倍的差异，这是相似的24 A分开。这里报道的O-17 NMR光谱代表了高场NMR技术的突破，该技术将在整个分子生物物理学中应用，因为O-17核对其化学环境的敏感性。
Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by O-17 NMR spectroscopy at 35.2 T (or 1,500 MHz for H-1) and computational studies. While backbone N-15 spectra clearly indicate structural symmetry between the two subunits, single site O-17 labels of the pore-lining carbonyls report two resonances, implying a break in dimer symmetry caused by the selective interactions with the water wire. The O-17 shifts document selective water hydrogen bonding with carbonyl oxygens that are stable on the millisecond timescale. Such interactions are supported by density functional theory calculations on snapshots taken from molecular dynamics simulations. Water hydrogen bonding in the pore is restricted to just three simultaneous interactions, unlike bulk water environs. The stability of the water wire orientation and its electric dipole leads to opposite charge-dipole interactions for K+ ions bound at the two ends of the pore, thereby providing a simple explanation for an similar to 20-fold difference in K+ affinity between two binding sites that are similar to 24 A apart. The O-17 NMR spectroscopy reported here represents a breakthrough in high field NMR technology that will have applications throughout molecular biophysics, because of the acute sensitivity of the O-17 nucleus to its chemical environment.