A competent catalytic active site is necessary for substrate induced dimer assembly in triosephosphate isomerase

Synergistic effect of compounds directed to triosephosphate isomerase, a combination to develop drug against trichomoniasis

The development of new drugs is continuous in the world; currently, saving resources (both economic ones and time) and preventing secondary effects have become a necessity for drug developers. Trichomoniasis is the most common nonviral sexually transmitted infection affecting more than 270 million people around the world. In our research group, we focussed on developing a selective and more effective drug against Trichomonas vaginalis, and we previously reported on a compound, called A4, which had a trichomonacidal effect. Later, we determined another compound, called D4, which also had a trichomonacidal effect together with favorable toxicity results. Both A4 and D4 are directed at the enzyme triosephosphate isomerase. Thus, we made combinations between the two compounds, in which we determined a synergistic effect against T. vaginalis, determining the IC₅₀ and the toxicity of the best relationship to obtain the trichomonacidal effect. With these results, we can propose a combination of compounds that represents a promising alternative for the development of a new therapeutic strategy against trichomoniasis.

Triosephosphate isomerase as a therapeutic target against trichomoniasis

Trichomoniasis is the most common non-viral sexually transmitted infection, caused by the protozoan parasite Trichomonas vaginalis, affecting millions of people worldwide. The main treatment against trichomoniasis is metronidazole and other nitroimidazole derivatives, but up to twenty percent of clinical cases of trichomoniasis are resistant to these drugs. In this study, we used high-performance virtual screening to search for molecules that specifically bind to the protein, triosephosphate isomerase from T. vaginalis (TvTIM). By in silico molecular docking analysis, we selected six compounds from a chemical library of almost 500,000 compounds. While none of the six inhibited the enzymatic activity of recombinant triosephosphate isomerase isoforms, one compound (A4; 3,3'-{[4-(4-morpholinyl)phenyl]methylene}bis(4- hydroxy-2H-chromen-2-one) altered their fluorescence emission spectra, suggesting that this chemical might interfere in an important non-glycolytic function of TvTIM. In vitro assays demonstrate that A4 is not cytotoxic but does have trichomonacidal impact on T. vaginalis cultures. With these results, we propose this compound as a potential drug with a new therapeutic target against Trichomonas vaginalis.

Esters of quinoxaline-7-carboxylate-1,4-di-N-oxide as Trichomonas vaginalis triosephosphate isomerase inhibitors

Trichomoniasis is a public health problem worldwide. Trichomoniasis treatment consists of the use of nitroimidazole derivatives; however, therapeutic ineffectiveness occurs in 5 to 20 % of the cases. Therefore, it is essential to propose new pharmacological agents against this disease. In this work, esters of quinoxaline-7-carboxylate-1,4-di-N-oxide (EQX-NO) were evaluated in in vitro assays as novel trichomonicidal agents. Additionally, an in vitro enzyme assay and molecular docking analysis against triosephosphate isomerase of Trichomonas vaginalis to confirm their mechanism of action were performed. Ethyl (compound 12) and n-propyl (compound 37) esters of quinoxaline-7-carboxy-late-1,4-di-N-oxide derivatives showed trichomonicidal activity comparable to nitazoxanide, whereas five methyl (compounds 5, 15, 19, 20 and 22), four isopropyl (compounds 28, 29, 30 and 34), three ethyl (compounds 4, 13 and 23) and one npropyl (compound 35) ester derivatives displayed activity comparable to albendazole. Compounds 6 and 20 decreased 100 % of the enzyme activity of recombinant protein triosephosphate isomerase.

The role of ligand-gated conformational changes in enzyme catalysis

Structural and biochemical studies on diverse enzymes have highlighted the importance of ligand-gated conformational changes in enzyme catalysis, where the intrinsic binding energy of the common phosphoryl group of their substrates is used to drive energetically unfavorable conformational changes in catalytic loops, from inactive open to catalytically competent closed conformations. However, computational studies have historically been unable to capture the activating role of these conformational changes. Here, we discuss recent experimental and computational studies, which can remarkably pinpoint the role of ligand-gated conformational changes in enzyme catalysis, even when not modeling the loop dynamics explicitly. Finally, through our joint analyses of these data, we demonstrate how the synergy between theory and experiment is crucial for furthering our understanding of enzyme catalysis.

Structural basis for the modulation of plant cytosolic triosephosphate isomerase activity by mimicry of redox-based modifications

Reactive oxidative species (ROS) and S-glutathionylation modulate the activity of plant cytosolic triosephosphate isomerases (cTPI). Arabidopsis thaliana cTPI (AtcTPI) is subject of redox regulation at two reactive cysteines that function as thiol switches. Here we investigate the role of these residues, AtcTPI-Cys13 and At-Cys218, by substituting them with aspartic acid that mimics the irreversible oxidation of cysteine to sulfinic acid and with amino acids that mimic thiol conjugation. Crystallographic studies show that mimicking AtcTPI-Cys13 oxidation promotes the formation of inactive monomers by reposition residue Phe75 of the neighboring subunit, into a conformation that destabilizes the dimer interface. Mutations in residue AtcTPI-Cys218 to Asp, Lys, or Tyr generate TPI variants with a decreased enzymatic activity by creating structural modifications in two loops (loop 7 and loop 6) whose integrity is necessary to assemble the active site. In contrast with mutations in residue AtcTPI-Cys13, mutations in AtcTPI-Cys218 do not alter the dimeric nature of AtcTPI. Therefore, modifications of residues AtcTPI-Cys13 and AtcTPI-Cys218 modulate AtcTPI activity by inducing the formation of inactive monomers and by altering the active site of the dimeric enzyme, respectively. The identity of residue AtcTPI-Cys218 is conserved in the majority of plant cytosolic TPIs, this conservation and its solvent-exposed localization make it the most probable target for TPI regulation upon oxidative damage by reactive oxygen species. Our data reveal the structural mechanisms by which S-glutathionylation protects AtcTPI from irreversible chemical modifications and re-routes carbon metabolism to the pentose phosphate pathway to decrease oxidative stress.