Energy and Structure of the M2 Helix in Acetylcholine Receptor-Channel Gating
Energy and Structure of the M2 Helix in Acetylcholine Receptor-Channel Gating
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DOI：
10.1016/j.bpj.2009.02.030
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发表时间：
2009-05-20
影响因子：
3.4
通讯作者：
Auerbach, Anthony
中科院分区：
文献类型：
--
作者：
Jha, Archana;Purohit, Prasad;Auerbach, Anthony
我们研究了单通道电流从神经肌肉乙酰胆碱受体通道突变的孔衬，M2螺旋的e-亚基。量化了三个参数：1）门控平衡常数（E-2）反映了C（losed）和O（pen）构象之间的能量差异，2）开放速率常数与E-2在对数-对数尺度上的相关性（Phi）反映了残基的能量特征（C-与O-样）;和3），开放通道电流振幅（i（o）），其报告突变是否改变离子渗透的能量学。在epsilon M2的细胞质一半（5 '、9'、12 '、13'和16 '）中观察到最大的E-2变化，对于>= 17'的残基则出现较小的变化。对于大多数E2 M2残基，Phi类似于0.54，但在具有最大E2变化的位置处为-0.32。精氨酸取代在六个位置显著减少，减少的幅度增加，16 '-> 2'。测量结果表明，9 '，12'和13'残基在通道开放过程中经历了大的和晚期的自由能变化。我们推测，在门控异构化中，朝向孔的残基>6'和
We studied single-channel currents from neuromuscular acetylcholine receptor-channels with mutations in the pore-lining, M2 helix of thee-subunit. Three parameters were quantified: 1), the diliganded gating equilibrium constant (E-2), which reflects the energy difference between C(losed) and O(pen) conformations; 2), the correlation between the opening rate constant and E-2 on a log-log scale (Phi), which illuminates the energy character of the residue (C- versus O-like) within the C O isomerization process; and 3), the open-channel current amplitude (i(o)), which reports whether a mutation alters the energetics of ion permeation. The largest E-2 changes were observed in the cytoplasmic half of epsilon M2 (5', 9', 12', 13', and 16'), with smaller changes apparent for residues >= 17'. Phi was similar to 0.54 for most epsilon M2 residues, but was -0.32 at the positions that had largest E2 changes. An arginine substitution reduced io significantly at six positions, with the magnitude of the reduction increasing, 16'-> 2'. The measurements suggest that the 9', 12', and 13' residues experience large and late free-energy changes in the channel-opening process. We speculate that in the gating isomerization the pore-facing residues >6' and