Preliminary crystallographic analysis of recombinant VapBC-15 toxin-antitoxin complex from Mycobacterium tuberculosis

The Mycobacterium tuberculosis vapBC15 locus encodes a toxin-antitoxin complex. VapC-15 is a toxin and possesses ribonuclease activity and VapB-15 is an antitoxin which both binds and inhibits the VapC-15 toxin. In this study, vapBC15 genes were cloned and co-expressed in Escherichia coli. The complex was purified to homogeneity by affinity and size-exclusion chromatography. The VapBC-15 complex was crystallized using the sitting-drop vapour-diffusion technique. The crystals diffracted to 2.6 Å resolution and belonged to space group P2₁2₁2₁, with unit-cell parameters a = 85.63, b = 139.09, c = 148.86 Å. The self-rotation function combined with Matthews coefficient and solvent-content calculations suggests the presence of either six or eight molecules of the complex in the asymmetric unit.