Molecular Cloning, Purification and Characterization of Mce1R of Mycobacterium tuberculosis

The mce1 operon of Mycobacterium tuberculosis, important for lipid metabolism/transport, host cell invasion, modulation of host immune response and pathogenicity, is under the transcriptional control of Mce1R. Hence characterizing Mce1R is an important step for novel anti-tuberculosis drug discovery. The present study reports functional and in silico characterization of Mce1R. In this work, we have computationally modeled the structure of Mce1R and have validated the structure by computational and experimental methods. Mce1R has been shown to harbor the canonical VanR-like structure with a flexible N-terminal 'arm', carrying conserved positively charged residues, most likely involved in the operator DNA binding. The mce1R gene has been cloned, expressed, purified and its DNA-binding activity has been measured in vitro. The K_d value for Mce1R-operator DNA interaction has been determined to be 0.35 ± 0.02 µM which implies that Mce1R binds to DNA with moderate affinity compared to the other FCD family of regulators. So far, this is the first report for measuring the DNA-binding affinity of any VanR-type protein. Despite significant sequence similarity at the N-terminal domain, the wHTH motif of Mce1R exhibits poor conservancy of amino acid residues, critical for DNA-binding, thus results in moderate DNA-binding affinity. The N-terminal DNA-binding domain is structurally dynamic while the C-terminal domain showed significant stability and such profile of structural dynamics is most likely to be preserved in the structural orthologs of Mce1R. In addition to this, a cavity has been detected in the C-terminal domain of Mce1R which contains a few conserved residues. Comparison with other FCD family of regulators suggests that most of the conserved residues might be critical for binding to specific ligand. The max pKd value and drug score for the cavity are estimated to be 9.04 and 109 respectively suggesting that the cavity represents a suitable target site for novel anti-tuberculosis drug discovery approaches.