与蛋白质调控DNA空穴迁移相关的具有负离解能特征的亚稳态氢键

利用密度泛函理论方法研究了作为空穴迁移载体的蛋白质复合的DNA三聚体(Protonated arginine…guanine…cytosine, ArgH⁺-GC)的氢键性质. 结果表明, 空穴迁移通过该载体单元时此类氢键表现为亚稳态, 且具有明显的负离解能. 正常情况下ArgH⁺基团在大小沟均能与GC碱对形成氢键, 且具有正的离解能. 然而, 当空穴转移至此将削弱氢键至亚稳态, 使之具有一定的离解势垒和负的离解能. 这种势垒抑制的负离解能现象意味着由于空穴俘获导致此三聚体结构单元在它的ArgH⁺…N7/O6键区储存了一定的能量(约108.78 kJ/mol). 该氢键离解通道受控于此键区两个相关组分之间的静电排斥和氢键吸引之间的平衡以及这两个相反作用随氢键距离不同的衰减速率. 基于电子密度分布的拓扑性质以及键临界点的Laplacian数值分析澄清了此类特殊的能量现象主要源自通过高能氢键(ArgH⁺…N7/O6)连接的授受体间的静电排斥. 进一步空穴俘获诱导的G→C质子转移可扩展负离解能区至ArgH⁺…N7/O6和Watson-Crick(WC) 氢键区. 另外, ArgH⁺ 结合到GC的大小沟增加其电离势, 因此削弱其空穴传导能力, 削弱程度取决于ArgH⁺与GC的距离. 推而广之, 在protonated lysine-GC和protonated histidine-GC体系也可观察到类似的现象. 显然, 此类性质可调的亚稳态氢键可调控DNA空穴迁移机理. 此工作为理解蛋白质调控的DNA空穴迁移机理提供了重要的能量学信息.

Metastable Hydrogen-bonds Featuring Negative Dissociation Energies in Protein-bound DNA in Hole Migration

We theoretically investigated the properties of hydrogen bonds in the protein-bound DNA trimer(protona-ted arginine…guanine…cytosine, ArgH⁺-GC) units as hole migration carriers using density functional theory calculations. Results suggest these hydrogen bonds are metastable and feature considerable negative dissociation energies upon hole migration through the ArgH⁺-GC units of the carriers. Normally, the ArgH⁺ group can H-bond with the guanine-cytosine(GC) base pair in the major/minor-groove face with positive dissociation energy. However, hole trapping weakens the H-bonds to being metastable with a mild dissociation barrier and considerable negative dissociation energy. This barrier-inhibited negative dissociation energy phenomenon implies that the trimer motif can store energy(ca.108.48 kJ/mol) in its ArgH⁺…N7/O6 bond zone due to hole-trapping. This H-bond dissociation channel is governed by a balance between electrostatic repulsion and H-bonding attraction in the two associated moieties and different attenuations of two opposite interactions with respect to the H-bond distance. The topological properties of electron densities and the Laplacian values at the bond critical points clarify that this energetic phenomenon mainly originates from additional electrostatic repulsions between two moieties linked via high-energy H-bonds(ArgH⁺…N7/O6). Proton transfer from G induced by hole-trapping can expand the negative dissociation energy zone to both the ArgH⁺…N7/O6 and Watson-Crick(WC) H-bond zones. In addition, the placement of ArgH⁺ at the major/minor grooves of DNA where ArgH⁺ could interact with the GC unit increases its ionization potential, and thus weakens its hole-relaying ability in different degrees, depending on the separation between ArgH⁺ and GC. Similar phenomena can be observed in the protonated lysine-GC and protonated histidine-GC cases. Clearly, such property-tunable metastable H-bonds can regulate the hole migration mechanism. This work provides some important energetic information for understanding the protein-regulated hole migration mechanism in DNA.