Stochastic theory of ion movement in channels with single-ion occupancy. Application to sodium permeation of gramicidin channels.
Stochastic theory of ion movement in channels with single-ion occupancy. Application to sodium permeation of gramicidin channels.
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单离子占据通道中离子运动的随机理论。
DOI：
10.1016/s0006-3495(87)83186-7
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发表时间：
1987
影响因子：
3.4
通讯作者：
Chiu,SW
中科院分区：
文献类型：
--
作者：
Jakobsson,E;Chiu,SW
通过Levitt的分析方法和布朗动力学模拟求解了单离子通道的电扩散方程。对于这两种类型的计算，假设浴槽和通道末端之间的离子分布平衡。发现潜在的配置文件，给很好的适合发表的数据Na+渗透短杆菌肽通道。数据最适合的配置文件，没有相对能量最大值在河口的通道。这一发现表明，响应于离子的接近，通道内的沃茨或通道带电基团的排列可以提供能量上有利的进入情况，足以克服去除大量水合沃茨所需的能量。另一种可能性是离子进入的屏障位于限制单离子占据的区域之外。取代缬氨酸与更多的极性氨基酸在1号位置被发现对应于加深的潜在的最小值附近的通道口，增加的高度的中央障碍离子易位通过通道，并可能减少在通道中的离子-水复合物的流动性。Levitt理论被扩展到计算离子穿过通道的通过时间和进入通道但没有穿过的离子的阻挡效应。这些量也计算布朗动力学方法。
The electrodiffusion equations were solved for the one-ion channel both by the analytical method due to Levitt and also by Brownian dynamic simulations. For both types of calculations equilibration of ion distribution between the bath and the ends of the channel was assumed. Potential profiles were found that give good fits to published data on Na+ permeation of gramicidin channels. The data were best fit by profiles that have no relative energy maximum at the mouth of the channel. This finding suggests that alignment of waters or channel charged groups inside the channel in response to an ion's approach may provide an energetically favorable situation for entry sufficient to overcome the energy required for removing bulk waters of hydration. An alternative possibility is that the barrier to ion entry is situated outside the region restricted to single-ion occupancy. Replacement of valine with more polar amino acids at the No. 1 location was found to correspond to a deepening of the potential minima near the channel mouths, an increase in height of the central barrier to ion translocation across the channel, and possibly a reduction in the mobility of the ion-water complex in the channel. The Levitt theory was extended to calculate passage times for ions to cross the channel and the blocking effects of ions that entered the channel but didn't cross. These quantities were also calculated by the Brownian dynamics method.