Interaction between Gallotannin and a Recombinant Form of Arginine Kinase of Trypanosoma brucei: Thermodynamic and Spectrofluorimetric Evaluation

Apoferritin and Apoferritin-Capped Metal Nanoparticles Inhibit Arginine Kinase of Trypanosoma brucei

The aim of this study was to explore the inhibitory potential of apoferritin or apoferritin-capped metal nanoparticles (silver, gold and platinum) against Trypanosomabrucei arginine kinase. The arginine kinase activity was determined in the presence and absence of apoferritin or apoferritin-capped metal nanoparticles. In addition, kinetic parameters and relative inhibition of enzyme activity were estimated. Apoferritin or apoferritin-capped metal nanoparticles’ interaction with arginine kinase of T. brucei led to a >70% reduction in the enzyme activity. Further analysis to determine kinetic parameters suggests a mixed inhibition by apoferritin or apoferritin-nanoparticles, with a decrease in V_max. Furthermore, the K_m of the enzyme increased for both ATP and L-arginine substrates. Meantime, the inhibition constant (K_i) values for the apoferritin and apoferritin-nanoparticle interaction were in the submicromolar concentration ranging between 0.062 to 0.168 nM and 0.001 to 0.057 nM, respectively, for both substrates (i.e., L-arginine and ATP). Further kinetic analyses are warranted to aid the development of these nanoparticles as selective therapeutics. Also, more studies are required to elucidate the binding properties of these nanoparticles to arginine kinase of T. brucei.

Arginine kinase shows nucleoside diphosphate kinase-like activity toward deoxythymidine diphosphate

Arginine kinase (AK) (ATP: L-arginine phosphotransferase, E.C. 2.7.3.3) catalyzes the reversible transfer of ATP γ-phosphate group to L-arginine to synthetize phospho-arginine as a high-energy storage. Previous studies suggest additional roles for AK in cellular processes. Since AK is found only in invertebrates and it is homologous to creatine kinase from vertebrates, the objective of this work was to demonstrate nucleoside diphosphate kinase-like activity for shrimp AK. For this, AK from marine shrimp Litopenaeus vannamei (LvAK) was purified and its activity was assayed for phosphorylation of TDP using ATP as phosphate donor. Moreover, by using high-pressure liquid chromatography (HPLC) the phosphate transfer reaction was followed. Also, LvAK tryptophan fluorescence emission changes were detected by dTDP titration, suggesting that the hydrophobic environment of Trp 221, which is located in the top of the active site, is perturbed upon dTDP binding. The kinetic constants for both substrates Arg and dTDP were calculated by isothermal titration calorimetry (ITC). Besides, docking calculations suggested that dTDP could bind LvAK in the same cavity where ATP bind, and LvAK basic residues (Arg124, 126 and 309) stabilize the dTDP phosphate groups and the pyrimidine base interact with His284 and Ser122. These results suggest that LvAK bind and phosphorylate dTDP being ATP the phosphate donor, thus describing a novel alternate nucleoside diphosphate kinase-like activity for this enzyme.