Investigation of potential hinge region for <i>Mycobacterium tuberculosis</i> topoisomerase I conformational change during catalysis

<i>Mycobacterium tuberculosis</i> topoisomerase I (MtbTOP1) is essential for the viability of the causative agent of TB. There are still significant unanswered questions regarding the dynamic conformations during catalysis of relaxation of negatively supercoiled DNA by MtbTOP1. We aim to study the flexible hinge residues that control the dynamics of inter-domain rearrangements involved in the enzyme conformational changes that allow the opening-closing of the topoisomerase gate. We used the online server PACKMAN to predict possible hinges from the MtbTOP1 crystal structure. The predicted region "PRO506 to LEU526" at the border between domains D2 and D4 with a p-value <0.05 was then studied as a potential hinge. The highly conserved ARG516 from this region interacts with the DNA inside the protein toroidal cavity. This arginine maintains inter-domain interaction with GLU207 of D4 and ASP691 of D5 domains. After introducing alanine substitutions, we further studied the mutant topoisomerases in biochemical experiments. The results showed a significant loss in DNA relaxation activity without affecting DNA binding and cleavage after mutating GLU207 and ARG516, consistent with their role as hinge residues in domain rearrangements.