Structural and Functional Study on DNA binding of MazE2 from Mycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis was first discovered by Robert Koch in 1882 and is a human infectious strain that causes lung disease through the respiratory tract. M. tuberculosis differs from ordinary bacteria in that it has thick membranes on the cell surface and does not stain Gram stain. However, when stained with Ziehl-Neelsen, it is difficult to decolorize by acid, alcohol and boiling, and this property is called acid-fast. Gram staining is negative, but they do not have external membranes and are classified as acid-fast gram-positive bacteria. Treatment of patients infected with M. tuberculosis is mainly medication. Isoniazid, rifampin, and pyrazinamide are used, and streptomycin is also used. Mycobacterium tuberculosis has the largest number of Toxin-Antitoxin system pairs among bacteria. The Toxin-Antitoxin system is classified into six types according to antitoxin properties. The target protein Rv0660c of this study is MazE, an antitoxin of MazEF system, which is one of Type2 Toxin-Antitoxin system. The Toxin-Antitoxin system plays a role in inhibiting the growth of bacteria or leading to death by external stimuli-activated toxins. Antitoxin normally binds to toxin and inhibits the activity of toxin. but it breaks down in extreme situations. Thus, dissociated toxin induces growth inhibition and death. This also induces latency and lowers susceptibility to antibiotics. We overexpress the N1-44 construct of Rv0660c to characterize the tertiary structure of this Rv0660c protein. His-tagged Rv0660c protein was purified using Immobilized Metal Affinity Chromatography (IMAC), and the His-tag was removed through thrombin cutting to further increase the protein purity. As a result, the crystal could be made and the structure could be obtained with a high resolution of 1.69 Å. The DNA binding experiments of Rv0660c were carried out by NMR and EMSA. Rv0660c was labeled with 13C and 15N isotopes. Heteronuclear multidimensional NMR spectra were measured and backbone assignments were made through HNCO, HNCA, HNCACO, HNCOCA, HNCOCACB and HNCACB spectra. The TALOS program was used to predict the secondary structure and identify the parts which interact DNA through DNA titration. We confirmed the binding of Rv0660c with DNA in vitro from Electrophoretic Mobility Shift Assay (EMSA).