The role of Ca2+ in the activity of Mycobacterium tuberculosis DNA gyrase
DNA gyrase is the only type II topoisomerase in Mycobacterium tuberculosis and needs to catalyse DNA supercoiling, relaxation and decatenation reactions in order to fulfil the functions normally carried out by gyrase and DNA topoisomerase IV in other bacteria. We have obtained evidence for the existence of a Ca2+-binding site in the GyrA subunit of M. tuberculosis gyrase. Ca2+ cannot support topoisomerase reactions in the absence of Mg2+, but partial removal of Ca2+ from GyrA by dialysis against EGTA leads to a modest loss in relaxation activity that can be restored by adding back Ca2+. More extensive removal of Ca2+ by denaturation of GyrA and dialysis against EGTA results in an enzyme with greatly reduced enzyme activities. Mutation of the proposed Ca2+-binding residues also leads to loss of activity. We propose that Ca2+ has a regulatory role in M. tuberculosis gyrase and suggest a model for the modulation of gyrase activity by Ca2+ binding.
[…] ClustalW () and MUSCLE (EMBL-EBI) (,) were used for multiple sequence alignment, PSIPRED () was used for protein secondary structure prediction and PROSITE was used for predicting structural and functional patterns (). Phyre (), BioInfoBank MetaServer () and Insight II (Accelrys) were used for molecular modelling studies. […]