Open Access Dissertation
Date of Award
G. Andres Cisneros
H. Bernhard Schlegel
This work describes the fundamental study of two enzymes of Fe(II)/-KG super family enzymes (TET2 and AlkB) by applying MD and QM/MM approaches, as well as the development of multipolar-polarizable force field (AMOEBA/GEM-DM) for condensed systems (ionic liquids and water).
TET2 catalytic activity has been studied extensively to identify the potential source of its substrate preference in three iterative oxidation steps. Our MD results along with some experimental data show that the wild type TET2 active site is shaped to enable higher order oxidation. We showed that the scaffold stablished by Y1902 and T1372 is required for iterative oxidation. The mutation of these residues perturbs the alignment of the substrate in the active site, resulting in “5hmC-stalling” phenotype in some of the mutants. We provided more details on 5hmC to 5fC oxidation mechanism for wild type and one of the “5hmC-stallling” mutants (E mutant). We showed that 5hmC oxidizes to 5fC in the wild type via three steps. The first step is the hydrogen atom abstraction from hydroxyl group of 5hmC, while the second hydrogen is transferred from methylene group of 5hmC through the third transition state as a proton. Our results suggest that the oxidation in E mutant is kinetically unfavorable due to its high barrier energy. Many analyses have been performed to qualitatively describe our results and we believed our results can be used as a guide for other researchers.
In addition, two MD approaches (explicit ligand sampling and WHAM) are used to study the oxygen molecule diffusion into the active site of AlkB. Our results showed that there are two possible channels for oxygen diffusion, however, diffusion through one of them is thermodynamically favorable. We also applied multipolar-polarizable force field to describe the oxygen diffusion along the preferred tunnel. We showed that the polarizable force field can describe the behavior of the highly polarizable systems accurately.
We also developed a new multipolar-polarizable force field (AMOEBA/GEM-DM) to calculate the properties of imidazolium- and pyrrolidinium- based ionic liquids and water in a range of temperature. Our results agree well with the experimental data. The good agreement between our results and experimental data is because our new parameters provide an accurate description of non-bonded interactions. We fit all the non-bonded parameters against QM. We use the multipoles extracted from fitted electron densities (GEM) and we consider both inter- and intra-molecular polarization. We believe this method can accurately calculate the properties of condensed systems and can be helpful for designing new systems such as electrolytes.
Torabifard, Hedieh, "Classical And Quantum Mechanical Simulations Of Condensed Systems And Biomolecules" (2017). Wayne State University Dissertations. 1884.