Water-Mediated Oxidation of Guanine by a Repair Enzyme: Simulation Using the ABEEM Polarizable Force Field.

ABSTRACT

The recognition mechanism of oxidative damage in organisms has long been a research hotspot. Water is an important medium in the recognition process, but its specific role remains unknown. There is a need to develop a suitable force field that can adequately describe the electrostatic, hydrogen bond, and other interactions among the molecules in the complex system of the repair enzyme and oxidized base. The developing ABEEM polarizable force field (PFF) has been used to simulate the repaired enzyme hOGG1 and oxidized DNA (PDB ID 1EBM) in a biological environment, and the corresponding results are better than those of the fixed-charge force fields OPLS/AA and AMBER OL15. 8-Oxo-G is recognized by Gln315 of hOGG1 mainly through hydrogen bonds mediated by continuous exchange of 2 water molecules. Phe319 and Cys253 are stacked on both sides of the π planes of bases to form sandwich structures. The charge polarization effect gives an important signal to drive the exchange of water molecules and maintains the recognition of oxidation bases by enzymes. The mediated main water molecule A and mediated auxiliary water molecule B together pull Gln315 to recognize 8-oxo-G by hydrogen bond interactions. Then, the charge polarization signal of solvent water molecule C with a large absolute charge causes the absolute charge of O atoms in water molecule A or B to increase by approximately 0.2 e, and water molecule A or B leaves Gln315 and 8-oxo-G. The other water molecule and water molecule C synergistically recognize 8-oxo-G with Gln315. Even though the water molecules between Gln315 and 8-oxo-G are removed, the MD simulation results show that water molecules appear between Gln315 and 8-oxo-G in a very short time (<2 ps). The dwell time of each water molecule is approximately 60 ps. The radial distribution function and dwell time support the correctness of the above mechanism. These polarization effects and hydrogen bonding interactions cannot be simulated by a fixed-charge force field.