Crystallization and preliminary X-ray diffraction analysis of biotin acetyl-CoA carboxylase ligase (BirA) from Mycobacterium tuberculosis

The gene encoding biotin acetyl-CoA carboxylase ligase (BirA) from Mycobacterium tuberculosis was cloned and expressed in Escherichia coli with a C-terminal Strep-tag. PEG 4000 as well as PEG 8000 were used as precipitants at pH 7.5 to crystallize the protein using the vapour-diffusion technique. X-ray characterization of crystals at room temperature indicated that the crystals belonged to the orthorhombic space group P2<SUB>1</SUB>2<SUB>1</SUB>2<SUB>1</SUB>, with unit-cell parameters a = 79.7, b = 62.8, c = 105.8 &#197; . Assuming the presence of two BirA molecules in the asymmetric unit, the solvent content of the crystals was 44% (V<SUB>M</SUB> = 2.2 &#197; <SUP>3</SUP> Da<SUP>-1</SUP>). When transferred to a cryoprotectant, crystals grown in the same drop exhibited a difference in one unit-cell parameter, with a = 60.1, b = 64.0, c = 103.6 &#197; , but belonged to the same P2<SUB>1</SUB>2<SUB>1</SUB>2<SUB>1</SUB> space group. These crystals, with two molecules of BirA present per asymmetric unit, appeared to have a very low solvent content of 28% (V<SUB>M</SUB> = 1.7 &#197; <SUP>3</SUP> Da<SUP>-1</SUP>)