Expression, crystallization and preliminary X-ray crystallographic analysis of D-alanine-D-alanine ligase from OXA-23-producing Acinetobacter baumannii K0420859

Acinetobacter baumannii causes bacteraemia, pneumonia, other respiratory-tract and urinary-tract infections in humans. OXA-23 carbapenemase-producing A. baumannii K0420859 (A. baumannii OXA-23) is resistant to carbapenem, a common antibacterial drug. To develop an efficient and novel antibacterial drug against A. baumannii OXA-23, D-alanine-D-alanine ligase, which is essential in bacterial cell-wall synthesis, is of interest. Here, the D-alanine-D-alanine ligase (AbDdl) gene from A. baumannii OXA-23 was cloned and expressed, and the AbDdl protein was purified and crystallized; this enzyme can be used as a novel target for an antibacterial drug against A. baumannii OXA-23. The AbDdl crystal diffracted to a resolution of 2.8 Å and belonged to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 113.4, b = 116.7, c = 176.5 Å, a corresponding V_M of 2.8 Å³ Da^-1 and a solvent content of 56.3%, and six protomers in the asymmetric unit.