Effective charge and free energy of DNA inside an ion channel
Effective charge and free energy of DNA inside an ion channel
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DOI：
10.1103/physreve.75.021906
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发表时间：
2007-02-01
影响因子：
2.4
通讯作者：
Shklovskii, B. I.
中科院分区：
文献类型：
--
作者：
Zhang, Jingshan;Shklovskii, B. I.
近年来，人们广泛研究了跨膜电压V驱动下单链DNA（ssDNA）通过脂质膜中α-溶血素通道的易位。虽然通道内ssDNA片段的裸电荷约为12（以电子电荷为单位），但不同有效电荷的测量结果为1至2之间的值。我们通过ssDNA和通道壁之间狭窄的充满水的间隙中电荷的大自能来解释这些具有挑战性的观察结果，这与水和脂质的介电常数之间的巨大差异有关，并计算ssDNA的有效电荷。我们从最基本的失速电荷q（s）开始，它决定了使DNA失速的力F-s=q（s）V/L相对于电压V（L是沟道的长度）。我们发现，失速电荷q（s）是成正比的离子电流被DNA，这是由于自能垒小。大电压V降低了DNA分子为了进入通道而应该克服的捕获势垒，通过与V平行的q（c），其中q（c）是有效捕获电荷。我们用失速载荷q（s）来表示。我们还将停滞电荷q（s）与在后端具有发夹的ssDNA测量的另外两个有效电荷相关联：负责发夹解链的势垒减少的电荷q（u）和负责DNA在发夹方向上抵抗电压逃逸的电荷q（e）。在小V，我们解释减少的捕获势垒与盐浓度。
Translocation of a single stranded DNA (ssDNA) through an alpha-hemolysin channel in a lipid membrane driven by applied transmembrane voltage V was extensively studied recently. While the bare charge of the ssDNA piece inside the channel is approximately 12 (in units of electron charge) measurements of different effective charges resulted in values between one and two. We explain these challenging observations by a large self-energy of a charge in the narrow water filled gap between ssDNA and channel walls, related to large difference between dielectric constants of water and lipid, and calculate effective charges of ssDNA. We start from the most fundamental stall charge q(s), which determines the force F-s=q(s)V/L stalling DNA against the voltage V (L is the length of the channel). We show that the stall charge q(s) is proportional to the ion current blocked by DNA, which is small due to the self-energy barrier. Large voltage V reduces the capture barrier which DNA molecule should overcome in order to enter the channel by parallel to q(c)parallel to V, where q(c) is the effective capture charge. We expressed it through the stall charge q(s). We also relate the stall charge q(s) to two other effective charges measured for ssDNA with a hairpin in the back end: the charge q(u) responsible for reduction of the barrier for unzipping of the hairpin and the charge q(e) responsible for DNA escape in the direction of hairpin against the voltage. At small V we explain reduction of the capture barrier with the salt concentration.