Simulating Enzyme Catalysis

Chemistry is about transformations between compounds as the result of forming and breaking bonds between their atoms. A detailed knowledge of these processes should open the door to one of the most desired goals in this field, which is the control of the rate constants that govern the time dependence of the concentrations of reactants and products. Changes in the concentration and preparation of the reactants, the nature of the solvents and external conditions (such as pressure and temperature) can be employed to speed up or slow down a chemical reaction. One of the major breakthroughs in the field of chemical kinetics was achieved when it was recognized that certain substances, the catalysts , were able to accelerate chemical reactions without being consumed during the process

Substrate promiscuity in DNA methyltransferase M.PvuII. A mechanistic insight

M.PvuII is a DNA methyltransferase from the bacterium Proteus vulgaris that catalyzes methylation of cytosine at the N4 position. This enzyme also displays promiscuous activity catalyzing methylation of adenine at the N6 position. In this work we use QM/MM methods to investigate the reaction mechanism of this promiscuous activity. We found that N6 methylation in M.PvuII takes place by means of a stepwise mechanism in which deprotonation of the exocyclic amino group is followed by the methyl transfer. Deprotonation involves two residues of the active site, Ser53 and Asp96, while methylation takes place directly from the AdoMet cofactor to the target nitrogen atom. The same reaction mechanism was described for cytosine methylation in the same enzyme, while the reversal timing, that is methylation followed by deprotonation, has been described in M.TaqI, an enzyme that catalyzes the N6-adenine DNA methylation from Thermus aquaticus. These mechanistic findings can be useful to understand the evolutionary paths followed by N-methyltransferases.This work was supported by the Ministerio de Ciencia e Innovación project CTQ2009-14541-C02-02, Generalitat Valenciana projects ACOMP/2011/028, ACOM/2012/243, GV/2012/053 and Universitat de Valencia project UV-INV-AE11-40931. J.A. and M.R. thank Ministerio Ciencia e Innovación for a doctoral grant and a ‘Juan de la Cierva’ contract, respectively. The authors acknowledge computational facilities of the Servei d’Informàtica de la Universitat de València in the ‘Tirant’ supercomputer, which is part of the Spanish Supercomputing Network

Are there dynamical effects in enzyme catalysis? Some thoughts concerning the enzymatic chemical step

AbstractWe offer some thoughts on the much debated issue of dynamical effects in enzyme catalysis, and more specifically on their potential role in the acceleration of the chemical step. Since the term ‘dynamics’ has been used with different meanings, we find it useful to first return to the Transition State Theory rate constant, its assumptions and the choices it involves, and detail the various sources of deviations from it due to dynamics (or not). We suggest that much can be learned about the key current questions for enzyme catalysis from prior extensive studies of dynamical and other effects in the case of reactions in solution. We analyze dynamical effects both in the neighborhood of the transition state and far from it, together with the situation when quantum nuclear motion is central to the reaction, and we illustrate our discussion with various examples of enzymatic reactions

Computational strategies for the design of new enzymatic functions

In this contribution, recent developments in the design of biocatalysts are reviewed with particular emphasis in the de novo strategy. Studies based on three different reactions, Kemp elimination, Diels–Alder and Retro-Aldolase, are used to illustrate different success achieved during the last years. Finally, a section is devoted to the particular case of designed metalloenzymes. As a general conclusion, the interplay between new and more sophisticated engineering protocols and computational methods, based on molecular dynamics simulations with Quantum Mechanics/Molecular Mechanics potentials and fully flexible models, seems to constitute the bed rock for present and future successful design strategies.This work was supported by the Spanish Ministerio de Economía y Competitividad for project CTQ2012-36253-C03, Universitat Jaume I – Spain (project P1·1B2014-26), Generalitat Valenciana – Spain (PROMETEOII/2014/022 and ACOMP/2014/277 projects), Polish National Center for Science (NCN) (grant 2011/02/A/ST4/00246, 2012−2017), the Polish Ministry of Science and Higher Education (“Iuventus Plus” program project no. 0478/IP3/2015/73, 2015-2016) and the USA National Institute of Health (ref. NIH R01 GM065368). Authors acknowledge computational resources from the Servei d’Informàtica of Universitat de València on the ‘Tirant’ supercomputer and the Servei d’Informat̀ica of Universitat Jaume I

Reversibility and Diffusion in Mandelythiamin Decarboxylation. Searching Dynamical Effects in Decarboxylation Reactions

Decarboxylation of mandelylthiamin in aqueous solution is analyzed by means of quantum mechanics/molecular mechanics simulations including solvent effects. The free energy profile for the decarboxylation reaction was traced, assuming equilibrium solvation, while reaction trajectories allowed us to incorporate nonequilibrium effects due to the solvent degrees of freedom as well as to evaluate the rate of the diffusion process in competition with the backward reaction. Our calculations that reproduce the experimental rate constant show that decarboxylation takes place with a non-negligible free energy barrier for the backward reaction and that diffusion of carbon dioxide is very fast compared to the chemical step. According to these findings catalysts would not act by preventing the backward reaction.GV/2012/053. ESTUDIO DEL MECANISMO DE REACCION Y DE LOS MOVIMIENTOS DINAMICOS DE LAS ENZIMAS ADN-METILTRANSFERASAS: CATALISIS Y INHIBICIO

Are Heme-Dependent Enzymes Always Using a Redox Mechanism? A Theoretical Study of the Kemp Elimination Catalyzed by a Promiscuous Aldoxime Dehydratase

The design of biocatalysts is a goal to improve the rate, selectivity and environmental friendship of chemical processes in biotechnology. In this regard, the use of computational techniques has provided valuable assistance in the design of enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM simulations have allowed getting an insight into the mechanism of a promiscuous aldoxime dehydratase (OxdA) for the Kemp elimination. We first demonstrate that, based on the use of linear response approximation (LRA) methods, the lowest energy electronic state of the benzisoxazole placed in the active sit of OxdA corresponds to a singlet state, being the triplet and the quintet state higher in energy. The presence of a heme group in the active site of the OxdA promiscuous enzyme opens the possibility of exploring a redox mechanism, similar to the one proposed in other reactions catalysed by heme-dependent enzymes. In addition, according to the geometrical analysis of the active site of this aldoxime dehydratase, the presence of a good base in the active site, His320, the proper pose of the substrate assisted by the porphyrin and an adequate electrostatic environment to stabilize the negative charge developed in the oxygen leaving group, makes available an acid/base mechanism. Comparison of the results derived from the exploration of both acid/base and redox mechanisms at B3LYP(Def2-TZVP)/MM level, shows how the later render the most favourable reaction path within the quintet state. The obtained activation free energy is in good agreement with the activation energy that can be deduced from the experimentally measured rate constant

Insights on the Origin of Catalysis on Glycine N-Methyltransferase from Computational Modeling

The origin of enzyme catalysis remains a question of debate despite much intense study. We report a QM/MM theoretical study of the SN2 methyl transfer reaction catalyzed by a glycine N-methyltransferase (GNMT) and three mutants to test whether recent experimental observations of rate-constant reductions and variations in inverse secondary α-3H kinetic isotope effects (KIEs) should be attributed to changes in the methyl donor−acceptor distance (DAD): is catalysis due to a compression effect? Semiempirical (AM1) and DFT (M06-2X) methods were used to describe the QM subset of atoms, while OPLS-AA and TIP3P classical force fields were used for the protein and water molecules, respectively. The computed activation free energies and KIEs are in good agreement with experimental data, but the mutations do not meaningfully affect the DAD: compression cannot explain the experimental variations on KIEs. On the contrary, electrostatic properties in the active site correlate with the catalytic activity of wild type and mutants. The plasticity of the enzyme moderates the effects of the mutations, explaining the rather small degree of variation in KIEs and reactivities

Molecular Mechanism of the site-specific self-cleavage of the RNA phosphodiester backbone by a Twister Ribozyme

Published as part of the special collection of articles derived from the 10th Congress on Electronic Structure: Principles and Applications (ESPA-2016).The catalytic activity of some classes of natural RNA, named as ribozymes, has been discovered just in the past decades. In this paper, the cleavage of the RNA phosphodiester backbone has been studied in aqueous solution and in a twister ribozyme from Oryza sativa. The free energy profiles associated with a baseline substrate-assisted mechanism for the reaction in the enzyme and in solution were computed by means of free energy perturbation methods within hybrid QM/MM potentials, describing the chemical system by the M06-2× functional and the environment by means of the AMBER and TIP3P force fields. The results confirm that this is a stepwise mechanism kinetically controlled by the second step that involves the P–O5′ breaking bond concomitant with the proton transfer from the OP1 atom to the leaving O5′ atom. 18O kinetic isotope effects on the nucleophile and leaving oxygen atoms, in very good agreement with experiments, also support this description. Nevertheless, the free energy profiles in the enzyme and in solution are almost coincident which, despite that the rate-limiting activation free energy is in very good agreement with experimental data of counterpart reactions in solution, rule out this substrate-assisted catalysis mechanism for the twister ribozyme from O. sativa. Catalysis must come from the role of alternative acid–base species not available in aqueous solution, but the rate-limiting transition state must be associated with the P–O5′ bond cleavage

Do zwitterionic species exist in the non-enzymatic peptide bond formation?

The use of proper computational methods and models has allowed answering the controversial question of whether zwitterionic species exist in the mechanism of peptide bond synthesis in aqueous solution. In fact, the different conformations of zwitterionic species open the door to different mechanistic paths

Theoretical Studies of the Self Cleavage Pistol Ribozyme Mechanism

Ribozymes are huge complex biological catalysts composed of a combination of RNA and proteins. Nevertheless, there is a reduced number of small ribozymes, the self-cleavage ribozymes, that are formed just by RNA and, apparently, they existed in cells of primitive biological systems. Unveiling the details of these "fossils" enzymes can contribute not only to the understanding of the origins of life but also to the development of new simplified artificial enzymes. A computational study of the reactivity of the pistol ribozyme carried out by means of classical MD simulations and QM/MM hybrid calculations is herein presented to clarify its catalytic mechanism. Analysis of the geometries along independent MD simulations with different protonation states of the active site basic species reveals that only the canonical system, with no additional protonation changes, renders reactive conformations. A change in the coordination sphere of the Mg2+ ion has been observed during the simulations, which allows proposing a mechanism to explain the unique mode of action of the pistol ribozyme by comparison with other ribozymes. The present results are at the center of the debate originated from recent experimental and theoretical studies on pistol ribozyme