Purification, crystallization and preliminary X-ray analysis of the periplasmic haem-binding protein HutB from Vibrio cholerae

The mechanism of haem transport across the inner membrane of pathogenic bacteria is currently insufficiently understood at the molecular level and no information is available for this process in Vibrio cholerae. To obtain structural insights into the periplasmic haem-binding protein HutB from V. cholerae (VcHutB), which is involved in haem transport through the HutBCD haem-transport system, at the atomic level, VcHutB was cloned, overexpressed and crystallized using 1.6 M ammonium sulfate as a precipitant at pH 7.0. X-ray diffraction data were collected to 2.4 angstrom resolution on the RRCAT PX-BL-21 beamline at the Indus-2 synchrotron, Indore, India. The crystals belonged to space group P4(3)2(1)2, with unit-cell parameters a = b = 62.88, c = 135.8 angstrom. Matthews coefficient calculations indicated the presence of one monomer in the asymmetric unit, with an approximate solvent content of 45.02%. Molecular-replacement calculations with Phaser confirmed the presence of a monomer in the asymmetric unit.