Crystallization and preliminary X-ray crystallographic analysis of a Mycobacterium tuberculosis ferritin homolog, BfrB

Mycobacterium tuberculosis (Mtb) is the causative agent of the deadly disease tuberculosis. Iron acquisition, regulation and storage are critical for the survival of this pathogen within a host. Thus, understanding the mechanisms of iron metabolism in Mtb will shed light on its pathogenic nature, as iron is important for infection. Ferritins are a superfamily of protein nanocages that function in both iron detoxification and storage, and Mtb contains both a predicted ferritin and a bacterioferritin. Here, the cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of the ferritin homolog (Mtb BfrB, Rv3841) is reported. An Mtb BfrB crystal grown at pH 6.5 using the hanging-drop vapor-diffusion technique diffracted to 2.50 A resolution and belonged to space group C2, with unit-cell parameters a = 226.2, b = 226.8, c = 113.7 A, beta = 94.7 degrees and with 24 subunits per asymmetric unit. Furthermore, modeling the crystal structure of a homologous ferritin into a low-resolution small-angle X-ray scattering (SAXS) electron-density envelope is consistent with the presence of 24 subunits in the BfrB protein cage quaternary structure.