title: The role of Ca²⁺ in the activity of Mycobacterium tuberculosis DNA gyrase.
abstract: 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 Ca(2+)-binding site in the GyrA subunit of M. tuberculosis gyrase. Ca(2+) cannot support topoisomerase reactions in the absence of Mg(2+), but partial removal of Ca(2+) from GyrA by dialysis against EGTA leads to a modest loss in relaxation activity that can be restored by adding back Ca(2+). More extensive removal of Ca(2+) by denaturation of GyrA and dialysis against EGTA results in an enzyme with greatly reduced enzyme activities. Mutation of the proposed Ca(2+)-binding residues also leads to loss of activity. We propose that Ca(2+) has a regulatory role in M. tuberculosis gyrase and suggest a model for the modulation of gyrase activity by Ca(2+) binding.
authors: Department of Biological Chemistry, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
authors: Shantanu
authors: S
authors: Karkare
authors: Faridoon
authors: F
authors: Yousafzai
authors: Lesley A
authors: LA
authors: Mitchenall
authors: Anthony
authors: A
authors: Maxwell
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000502:physiology*; D019295:Computational Biology; D053837:DNA Cleavage; D027081:DNA Gyrase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D008274:Magnesium; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D059748:Proteolysis; D016415:Sequence Alignment
chemical_list: D004278:DNA, Superhelical; D027081:DNA Gyrase; D008274:Magnesium; D002118:Calcium