Cloning, expression, purification, crystallization and preliminary X-ray studies of the C-terminal domain of Rv3262 (FbiB) from Mycobacterium tuberculosis

During cofactor F₄₂₀ biosynthesis, the enzyme F₄₂₀-γ-glutamyl ligase (FbiB) catalyzes the addition of γ-linked L-glutamate residues to form polyglutamyl­ated F₄₂₀ derivatives. In Mycobacterium tuberculosis, Rv3262 (FbiB) consists of two domains: an N-terminal domain from the F₄₂₀ ligase superfamily and a C-­terminal domain with sequence similarity to nitro-FMN reductase superfamily proteins. To characterize the role of the C-terminal domain of FbiB in polyglutamyl ligation, it has been purified and crystallized in an apo form. The crystals diffracted to 2.0 Å resolution using a synchrotron source and belonged to the tetragonal space group P4₁2₁2 (or P4₃2₁2), with unit-cell parameters a = b = 136.6, c = 101.7 Å, α = β = γ = 90°.