Zhang Jingshan, Shklovskii B I
Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2007 Feb;75(2 Pt 1):021906. doi: 10.1103/PhysRevE.75.021906. Epub 2007 Feb 15.
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 /q(c)/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.
最近，人们广泛研究了在施加的跨膜电压V驱动下，单链DNA（ssDNA）通过脂质膜中的α-溶血素通道的转运过程。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在1到2之间。我们通过ssDNA与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的巨大差异有关，并计算了ssDNA的有效电荷。我们从最基本的阻滞电荷q(s)开始，它决定了对抗电压V使DNA停滞的力F(s)=q(s)V/L（L是通道的长度）。我们表明，阻滞电荷q(s)与被DNA阻断的离子电流成正比，由于自能垒，该离子电流很小。大电压V降低了DNA分子进入通道时应克服的捕获势垒，降低量为/q(c)/V，其中q(c)是有效捕获电荷。我们通过阻滞电荷q(s)来表示它。我们还将阻滞电荷q(s)与在后端带有发夹的ssDNA测量的另外两个有效电荷联系起来：负责降低发夹解链势垒的电荷q(u)和负责DNA沿发夹方向逆电压逃逸的电荷q(e)。在小电压V下，我们解释了捕获势垒随盐浓度的降低。
