Search results for "dihydrofolate reductase"
showing 10 items of 15 documents
Heavy enzymes and the rational redesign of protein catalysts
2019
Abstract An unsolved mystery in biology concerns the link between enzyme catalysis and protein motions. Comparison between isotopically labelled “heavy” dihydrofolate reductases and their natural‐abundance counterparts has suggested that the coupling of protein motions to the chemistry of the catalysed reaction is minimised in the case of hydride transfer. In alcohol dehydrogenases, unnatural, bulky substrates that induce additional electrostatic rearrangements of the active site enhance coupled motions. This finding could provide a new route to engineering enzymes with altered substrate specificity, because amino acid residues responsible for dynamic coupling with a given substrate present…
Minimization of dynamic effects in the evolution of dihydrofolate reductase
2015
Protein isotope labeling is a powerful technique to probe functionally important motions in enzyme catalysis and can be applied to investigate the conformational dynamics of proteins.
DHFR Inhibitors: Reading the Past for Discovering Novel Anticancer Agents.
2019
Dihydrofolate reductase inhibitors are an important class of drugs, as evidenced by their use as antibacterial, antimalarial, antifungal, and anticancer agents. Progress in understanding the biochemical basis of mechanisms responsible for enzyme selectivity and antiproliferative effects has renewed the interest in antifolates for cancer chemotherapy and prompted the medicinal chemistry community to develop novel and selective human DHFR inhibitors, thus leading to a new generation of DHFR inhibitors. This work summarizes the mechanism of action, chemical, and anticancer profile of the DHFR inhibitors discovered in the last six years. New strategies in DHFR drug discovery are also provided, …
Exploring Chemical Reactivity in Enzyme Catalyzed Processes Using QM/MM Methods: An Application to Dihydrofolate Reductase
2015
Enzymes are the catalysts used by living organisms to accelerate chemical processes under physiological conditions. In this chapter, we illustrate the current view about the origin of their extraordinary rate enhancement based on molecular simulations and, in particular, on methods based on the combination of Quantum Mechanics and Molecular Mechanics potentials which provide a solution to treat the chemical reactivity of these large and complex molecular systems. Computational studies on Dihydrofolate Reductase have been selected as a conductor wire to present the evolution and difficulties to model chemical reactivity in enzymes. The results discussed here show that experimental observatio…
Photogenotoxicity of folic acid.
2013
Folic acid (FA), also named vitamin B9, is an essential cofactor for the synthesis of DNA bases and other biomolecules after bioactivation by dihydrofolate reductase (DHFR). FA is photoreactive and has been shown to generate DNA modifications when irradiated with UVA (360 nm) in the presence of DNA under cell-free conditions. To investigate the relevance of this reaction for cells and tissues, we irradiated three different cell lines (KB nasopharyngeal carcinoma cells, HaCaT keratinocytes, and a melanoma cell line) in the presence of FA and quantified cytotoxicity and DNA damage generation. The results indicate that FA is phototoxic and photogenotoxic by two different mechanisms. First, ext…
The SGLT2 inhibitor empagliflozin improves the primary diabetic complications in ZDF rats
2017
Hyperglycemia associated with inflammation and oxidative stress is a major cause of vascular dysfunction and cardiovascular disease in diabetes. Recent data reports that a selective sodium-glucose co-transporter 2 inhibitor (SGLT2i), empagliflozin (Jardiance®), ameliorates glucotoxicity via excretion of excess glucose in urine (glucosuria) and significantly improves cardiovascular mortality in type 2 diabetes mellitus (T2DM). The overarching hypothesis is that hyperglycemia and glucotoxicity are upstream of all other complications seen in diabetes. The aim of this study was to investigate effects of empagliflozin on glucotoxicity, β-cell function, inflammation, oxidative stress and endothel…
Protein isotope effects in dihydrofolate reductase from Geobacillus stearothermophilus show entropic-enthalpic compensatory effects on the rate const…
2014
Catalysis by dihydrofolate reductase from the moderately thermophilic bacterium Geobacillus stearothermophilus (BsDHFR) was investigated by isotope substitution of the enzyme. The enzyme kinetic isotope effect for hydride transfer was close to unity at physiological temperatures but increased with decreasing temperatures to a value of 1.65 at 5 °C. This behavior is opposite to that observed for DHFR from Escherichia coli (EcDHFR), where the enzyme kinetic isotope effect increased slightly with increasing temperature. These experimental results were reproduced in the framework of variational transition-state theory that includes a dynamical recrossing coefficient that varies with the mass of…
Candidate target mechanisms of the growth inhibitor cyromazine: Studies of phenylalanine hydroxylase, puparial amino acids, and dihydrofolate reducta…
2000
Cyromazine, an insect growth regulator, affects larval and pupal cuticles in dipterans and some other insects. The mode of action of this aminotriazine is not known yet, though it has been shown not to inhibit the synthesis of chitin and cuticular proteins. Cyromazine may, however, act on some step(s) of sclerotization of the cuticle. In the present study, we have analyzed the key enzyme for the production of sclerotization agents, phenylalanine hydroxylase (PAH), using the enzyme from Drosophila, a cyromazine-sensitive insect. PAH was studied in vitro with cyromazine and three biologically less active derivatives at concentrations ranging from 1 μM to 1 mM. None of the compounds did signif…
Increased dynamic effects in a catalytically compromised variant of Escherichia coli dihydrofolate reductase
2013
Isotopic substitution (15N, 13C, 2H) of a catalytically compromised variant of Escherichia coli dihydrofolate reductase, EcDHFR-N23PP/S148A, has been used to investigate the effect of these mutations on catalysis. The reduction of the rate constant of the chemical step in the EcDHFR-N23PP/S148A catalyzed reaction is essentially a consequence of an increase of the quasi-classical free energy barrier and to a minor extent of an increased number of recrossing trajectories on the transition state dividing surface. Since the variant enzyme is less well set up to catalyze the reaction, a higher degree of active site reorganization is needed to reach the TS. Although millisecond active site motion…
Quantifying the limits of transition state theory in enzymatic catalysis
2017
Significance Transition state theory (TST) is the most popular theory to calculate the rates of enzymatic reactions. However, in some cases TST could fail due to the violation of the nonrecrossing hypothesis at the transition state. In the present work we show that even for one of the most controversial enzymatic reactions—the hydride transfer catalyzed by dihydrofolate reductase—the error associated to TST represents only a minor correction to the reaction rate. Moreover, this error is actually larger for the reaction in solution than in the enzymatic active site. Based on this finding and on previous studies we propose an “enzymatic shielding” hypothesis which encompasses various aspects …