Expression, crystallization and preliminary X-ray analysis of a ferric binding protein from Thermus thermophilus HB8

A ferric binding protein from Thermus thermophilus HB8 (TtFbpA) was expressed, purified and crystallized using the hanging-drop vapour-diffusion method. Four different crystal forms were obtained and characterized by X-ray diffraction. Two crystal forms with TtFbpA in the apo state belonged to the orthorhombic space group P2₁2₁2₁ (unit-cell parameters a = 42.1, b = 139.3, c = 326.5 Å and a = 42.1, b = 139.3, c = 218.9 Å). The third form with TtFbpA also in the apo state belonged to the monoclinic space group P2₁ (unit-cell parameters a = 66.5, b = 61.7, c = 73.9 Å, β = 111.7°). The fourth form, with TtFbpA in the iron-bound holo state as confirmed by an atomic absorption spectrophotometry assay, belonged to the trigonal space group P3₁21 or P3₂21 (unit-cell parameters a = 63.6, b = 63.6, c = 266.7 Å, α = β = 90.0, γ = 120.0°).