pH-dependent conformation, dynamics, and aromatic interaction of the gating tryptophan residue of the influenza M2 proton channel from solid-state NMR.
pH-dependent conformation, dynamics, and aromatic interaction of the gating tryptophan residue of the influenza M2 proton channel from solid-state NMR.
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DOI：
10.1016/j.bpj.2013.02.054
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发表时间：
2013-04
影响因子：
3.4
通讯作者：
Jonathan K. Williams;Y. Zhang;K. Schmidt-Rohr;M. Hong
中科院分区：
文献类型：
--
作者：
Jonathan K. Williams;Y. Zhang;K. Schmidt-Rohr;M. Hong
流感病毒的M2蛋白在外部酸性pH下将质子传导到病毒粒子中。四聚体通道的质子选择性是由一个组氨酸(His37)控制的，而通道门控是由蛋白质跨膜区的一个色氨酸(Trp41)完成的。这两个功能残基之间的芳香族相互作用以前已经在拉曼光谱中观察到，但这种相互作用的原子分辨证据仍然很少。在这里，我们使用高分辨固体核磁共振波谱通过测量色氨酸化学位移、His37-Trp41距离和吲哚在高和低pH下的动力学来确定M2跨膜肽中Trp41的侧链构象和动力学。原子间距离限制Trp41侧链构象为转位χ1，转位χ2为12 0-135°。Th 90旋转体将吲哚的Nε1-Cε2-Cζ2侧指向水孔。在高pH和低pH之间，精确的χ1和χ2角相差∼20°。这些差异，加上已知的高和低pH之间螺旋倾斜角的变化，推动咪唑和吲哚环在低pH下更紧密地结合在一起。此外，测得的有序参数表明，吲哚环在酸性条件下同时发生χ-1和χ-2的扭转波动，而在高pH条件下仅受χ-1的限制。结果是，在低pH时，Trp41侧链与His37周期性地发生强的阳离子-π相互作用，而在高pH时，吲哚环离咪唑更远。这些结果为理解如何将核磁共振测量的His37-水质子交换速率还原为生化实验中测量的小质子通量提供了结构基础。吲哚动力学结合咪唑的已知运动表明，这种紧凑的离子通道使用经济的侧链动力学来调节质子的传导和门控。
The M2 protein of the influenza virus conducts protons into the virion under external acidic pH. The proton selectivity of the tetrameric channel is controlled by a single histidine (His37), whereas channel gating is accomplished by a single tryptophan (Trp41) in the transmembrane domain of the protein. Aromatic interaction between these two functional residues has been previously observed in Raman spectra, but atomic-resolution evidence for this interaction remains scarce. Here we use high-resolution solid-state NMR spectroscopy to determine the side-chain conformation and dynamics of Trp41in the M2 transmembrane peptide by measuring the Trp chemical shifts, His37-Trp41distances, and indole dynamics at high and low pH. The interatomic distances constrain the Trp41side-chain conformation totransforχ1and 120–135° forχ2. Thist90 rotamer points the Nε1-Cε2-Cζ2 side of the indole toward the aqueous pore. The preciseχ1andχ2angles differ by ∼20° between high and low pH. These differences, together with the known changes in the helix tilt angle between high and low pH, push the imidazole and indole rings closer together at low pH. Moreover, the measured order parameters indicate that the indole rings undergo simultaneousχ1andχ2torsional fluctuations at acidic pH, but only restrictedχ1fluctuations at high pH. As a result, the Trp41side chain periodically experiences strong cation-πinteractions with His37at low pH as the indole sweeps through its trajectory, whereas at high pH the indole ring is further away from the imidazole. These results provide the structural basis for understanding how the His37-water proton exchange rate measured by NMR is reduced to the small proton flux measured in biochemical experiments. The indole dynamics, together with the known motion of the imidazolium, indicate that this compact ion channel uses economical side-chain dynamics to regulate proton conduction and gating.