Methionine gamma lyase: Structure-activity relationships and therapeutic applications

Methionine gamma lyase (MGL) is a bacterial and plant enzyme that catalyzes the conversion of methionine in methanthiol, 2-oxobutanoate and ammonia. The enzyme belongs to fold type I of the pyridoxal 5'-dependent family. The catalytic mechanism and the structure of wild type MGL and variants were determined in the presence of the natural substrate as well as of many sulfur-containing derivatives. Structure-function relationship studies were pivotal for MGL exploitation in the treatment of cancer, bacterial infections, and other diseases. MGL administration to cancer cells leads to methionine starvation, thus decreasing cells viability and increasing their vulnerability towards other drugs. In antibiotic therapy, MGL acts by transforming prodrugs in powerful drugs. Numerous strategies have been pursued for the delivering of MGL in vivo to prolong its bioavailability and decrease its immunogenicity. These include conjugation with polyethylene glycol and encapsulation in synthetic or natural vesicles, eventually decorated with tumor targeting molecules, such as the natural phytoestrogens daidzein and genistein. The scientific achievements in studying MGL structure, function and perspective therapeutic applications came from the efforts of many talented scientists, among which late Tatyana Demidkina to whom we dedicate this review.

Pyridyl Methylsulfinyl Benzimidazole Derivatives as Promising Agents against Giardia lamblia and Trichomonas vaginalis

Protozoan parasites, such as Giardia lamblia and Trichomonas vaginalis, cause the most prevalent infections in humans in developing countries and provoke significant morbidity and mortality in endemic countries. Despite its side-effects, metronidazole is still the drug of choice as a giardiacidal and trichomonacidal tissue-active agent. However, the emergence of metronidazole resistance and its evolved strategies of parasites to evade innate host defenses have hindered the identification and development of new therapeutic strategies against these parasites. Here, we tested five synthesized benzimidazole derivatives as possible drugs for treating giardiasis and trichomoniasis, probing the bifunctional enzyme glucose 6-phosphate dehydrogenase::6-phosphogluconolactone from G. lamblia (GlG6PD::6PGL) and T. vaginalis (TvG6PD::6PGL) as a drug target. The investigated benzimidazole derivatives were H-B2M1, H-B2M2, H₂N-BZM6, O₂N-BZM7, and O₂N-BZM9. The recombinant enzymes were used in inhibition assays, and in silico computational predictions and spectroscopic studies were applied to follow the structural alteration of the enzymes and identify the possible mechanism of inhibition. We identified two potent benzimidazole compounds (O₂N-BZM7 and O₂N-BZM9), which are capable of inhibiting both protozoan G6PD::6PGL enzymes and in vitro assays with these parasites, showing that these compounds also affect their viability. These results demonstrate that other therapeutic targets of the compounds are the enzymes GlG6PD::6PGL and TvG6PD::6PGL, which contribute to their antiparasitic effect and their possible use in antigiardial and trichomonacidal therapies.

Biological chemistry of the carbon–sulfur bond

Carbon–sulfur biological chemistry encompasses a fascinating area of biochemistry and medicinal chemistry and includes the roles that methionine and S-adenosyl-l-methionine play in cells as well as the chemistry of intracellular thiols such as glutathione. This article, based on the 2014 Bernard Belleau Award lecture, provides an overview of some of the key investigations that were undertaken in this area from a bioorganic perspective. The research has ameliorated our fundamental knowledge of several of the enzymes utilizing these sulfur-containing molecules, has led to the development of several novel 19F biophysical probes, and has explored some of the medicinal chemistry associated with these processes.

Mechanistic studies on the enzymatic processing of fluorinated methionine analogues by Trichomonas vaginalis methionine γ-lyase

TFM (L-trifluoromethionine), a potential prodrug, was reported to be toxic towards human pathogens that express MGL (L-methionine γ-lyase; EC 4.4.1.11), a pyridoxal phosphate-containing enzyme that converts L-methionine into α-oxobutyrate, ammonia and methyl mercaptan. It has been hypothesized that the extremely reactive thiocarbonyl difluoride is produced when the enzyme acts upon TFM, resulting in cellular toxicity. The potential application of the fluorinated thiomethyl group in other areas of biochemistry and medicinal chemistry requires additional studies. Therefore a detailed investigation of the theoretical and experimental chemistry and biochemistry of these fluorinated groups (CF3S− and CF2HS−) has been undertaken to trap and identify chemical intermediates produced by enzyme processing of molecules containing these fluorinated moieties. TvMGL (MGL from Trichomonas vaginalis) and a chemical model system of the reaction were utilized in order to investigate the cofactor-dependent activation of TFM and previously uninvestigated DFM (L-difluoromethionine). The differences in toxicity between TFM and DFM were evaluated against Escherichia coli expressing TvMGL1, as well as the intact human pathogen T. vaginalis. The relationship between the chemical structure of the reactive intermediates produced from the enzymatic processing of these analogues and their cellular toxicity are discussed.