structures of dehydrated and hydrated BirA, at 2.69 A and 2.8 A resolution, respectively. Dehydration of BirA crystals traps both the apo and active conformations in its asymmetric unit. The crystal lattice rearrangement due to shrinkage in the dehydrated Mtb-BirA crystals ensues structural order of otherwise flexible ligand-binding loops L4 and L8 in apo BirA. In addition, crystal dehydration results in a shift of 3.5 A in the flexible loop L6, a proline-rich loop unique to Mycobacterium tuberculosis complex as well as around the L11 region. The shift in loop L11 in the C-terminal domain on dehydration emulates the action responsible for the complex formation with its protein ligand biotin carboxyl carrier protein domain of ACCA3. The two subunits A and B, though related by a noncrystallographic twofold symmetry, assemble into an asymmetric dimer representing the ligand-bound and ligand-free states of the protein, respectively |
Mycobacterium tuberculosis |