Monoclonal antibodies to mycobacterial DNA gyrase A inhibit DNA supercoiling activity

Abstract

DNA gyrase is an essential type II topoisomerase found in bacteria. We have previously characterized DNA gyrase from Mycobacterium tuberculosis and Mycobacterium smegmatis. In this study, several monoclonal antibodies were generated against the gyrase A subunit (GyrA) of M. smegmatis. Three, MsGyrA:C3, MsGyrA:H11 and MsGyrA:E9, were further analyzed for their interaction with the enzyme. The monoclonal antibodies showed high degree of crossreactivity with both fast-growing and slow-growing mycobacteria. In contrast, none recognized Escherichia coli GyrA. All the three monoclonal antibodies were of IgG 1 isotype falling into two distinct types with respect to epitope recognition and interaction with the enzyme. MsGyrA:C3and MsGyrA:H11 IgG, and their respective Fab fragments, inhibited the DNA supercoiling activity catalyzed by mycobacterial DNA gyrase. The epitope for the neutralizing monoclonal antibodies appeared to involve the region towards the N-terminus (residues 351±415) of the enzyme in a conformation-dependent manner. These monoclonal antibodies would serve as valuable tools for structure± function analysis and immunocytological studies of mycobacterial DNA gyrase. In addition, they would be useful for designing peptide inhibitors against DNA gyrase.Keywords: DNA gyrase; enzyme inhibition; epitope mapping; monoclonal antibody; mycobacterium.The topological state of DNA plays an important role in biological activity and is maintained by a group of enzymes called topoisomerases [1,2]. These enzymes change the topology of DNA by passing one segment through another. The type I enzymes catalyze DNA-strand passage by transiently breaking one strand at a time and type II enzymes create transient breaks in both strands of a DNA segment for the enzyme-mediated passage of the second segment [1±3]. Type II topoisomerases are essential cellular enzymes that function in the segregation of newly replicated chromosome pairs, chromosome condensation and in altering DNA superhelicity [4]. DNA gyrase is a type II topoisomerase exclusively found in prokaryotes. It is the only enzyme that can introduce negative supercoiling, in a reaction that depends on ATP hydrolysis. The enzyme also catalyzes a number of other topological interconversions such as knotting±unknotting and catenation±decatenation [3].DNA gyrase from Escherichia coli is composed of two subunits, A (GyrA) and B (GyrB). The active enzyme is a tetramer of two subunits each of GyrA and GyrB [5,6]. The GyrA subunit has the active site for DNA binding, cleavage and resealing, whereas GyrB powers the reaction by catalyzing ATP hydrolysis [7]. DNA gyrase is the target of two distinct classes of inhibitors, coumarins and quinolones. Coumarins bind to GyrB and are competitive inhibitors with respect to ATP. In contrast, quinolones bind DNA gyrase when the enzyme is complexed with DNA and trap the enzyme in an abortive ternary complex [8].Of the 50 species in the genus mycobacterium, about 20 are of medical importance. Apart from well-known human mycobacterial pathogen...

Identification of a nitroimidazo-oxazine-specific protein involved in PA-824 resistance in Mycobacterium tuberculosis

“…For Western blotting, cell lysates were prepared as described in ref. 28. Polyclonal antibodies to purified Mtb-FGD1-His were raised in rabbits (Biosource, Worcester, MA) and serum used at 1:20,000 dilution.…”

Cyclic AMP in Mycobacteria: Characterization and Functional Role of the Rv1647 Ortholog in Mycobacterium smegmatis

“…Membrane fractions were prepared from the complement strain and subjected to Western blot analysis using affinity-purified antibody to Rv1647 (35) and a monoclonal antibody to gyrase A characterized previously (23).…”

A monoclonal antibody that inhibits mycobacterial DNA gyrase by a novel mechanism

“…The supercoiling reactions were carried out as described previously (15). The IC 50 was defined as the concentration of the inhibitor that reduced the enzymatic activity observed with inhibitor-free controls by 50%.…”

“…Polyclonal antibodies raised against M.tuberculosis GyrA recognize GyrA proteins from other mycobacteria but not from E.coli (14). Monoclonal antibodies (mAbs) against the individual subunits of M.smegmatis gyrase have been raised and characterized (15,16). Two of these mAbs (C3 and H11) bind within the region between amino acids 351 and 415 of GyrA and have been shown to inhibit supercoiling by gyrase.…”

“…Two of these mAbs (C3 and H11) bind within the region between amino acids 351 and 415 of GyrA and have been shown to inhibit supercoiling by gyrase. A third antibody (E9) bound elsewhere and did not affect gyrase activity (15). In this paper, we have further investigated the mechanism of inhibition by one particular antibody, mAb:C3, and show that it inhibits the enzyme by a completely novel mechanism, which could be exploited to develop new agents for tuberculosis therapy.…”