ИСТИНА

Methionine g-lyase (MGL) is a pyridoxal 5’-phosphate dependent enzyme that catalyzes α,γ-elimination and γ-replacement reactions using L-methionine and its derivatives as substrates. It also catalyses α,β-elimination and β-replacement reactions of S-substituted L-cysteines. MGL found in some bacteria, in the family Enterobacteriaceae (Citrobacter freundii), as well as in other pathogenic organisms, such as Aeromonas sp., Clostridium sporogenes, Porphyromonas gingivalis. Absence of the enzyme in mammalian cells allows MGL to be considered as a potential drug target. Compounds for NMR screening tests were initially chosen by in silico docking. 32000 structures having carboxyl group were selected from a list of commercially available compounds. Virtual screening was performed using the program Algocomb with the modified TM scoring function. Crystal structure of C. freundii MGL (PDB code 3JWB) was used for the docking. 21 of 32000 compounds were selected for subsequent experimental tests. Selection was based on both score values and additional criteria, such as lipophility, limitation of the molar weight etc. NMR screening methods include Saturation Transfer Difference (STD) and WaterLOGSY (Water-ligand observed via gradient spectroscopy) experiments, as well as monitoring of the transverse relaxation rates of the ligand signals. STD and WaterLOGSY techniques allow distinguishing ligands, which are capable or not capable to bind a protein. NMR screening methods can be used to detect ligands within rather broad range of affinities (dissociation constants between 10-3 and 10-8 M). Since these methods are based on the observation of the signals from low-molecular weight compounds, high magnetic field NMR instruments are not required for such studies. STD and WaterLOGSY experiments were carried out on Bruker Avanvce 600 MHz instrument. The protein concentration range in NMR experiments was 7-14 μMol. STD and WaterLOGSY experiments allowed selecting 4 out of 21 compounds having the highest affinity to MGL. These compounds will be further checked on the inhibitory activity in vitro. Then 20 another compounds were chosen by docking to adjacent pocket, and 2 of them were selected by NMR screening experiments. Next step of research is to combine structure of chosen ligands into new ligand with much bigger affinity. Thus, the combination of virtual screening methods, NMR techniques based on the observation of signals of ligands that interact with biomolecules, and biochemical techniques, is proved an effective tool for searching the potential inhibitors of enzymes considered as promising biological targets.