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Acinetobacter baumannii has received much attention owing to its exceptional ability to develop resistance to currently available antibiotics. Alanine racemase (ALR) catalyzes the racemization of L-alanine to D-alanine with pyridoxal 5'-phosphate (PLP) as a cofactor. The D-alanine product is an essential component of the bacterial cell wall and ALR is a potential target for the development of novel antibacterial drugs. The alr gene from A. baumannii was cloned and the protein (AbALR) was expressed, purified and crystallized. The AbALR crystal diffracted to 2.3 Å resolution and belonged to the primitive orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 55.1, b = 85.0, c = 167.7 Å. Two protomers were present in the asymmetric unit, with a corresponding V(M) value of 2.3 Å(3) Da(-1) and a solvent content of 47.5%.

Alanine racemase (Alr(MB4)), a dimeric PLP-dependent thermostable enzyme from the anaerobic eubacterium Thermoanaerobacter tengcongensis MB4, was expressed and purified with a His(6) tag in a form suitable for X-ray crystallographic analysis. Crystals were grown by the hanging-drop vapour-diffusion method at 289 K using a solution consisting of 0.1 M bis-tris pH 7.0, 22%(w/v) polyethylene glycol 4000. X-ray diffraction data were collected to 2.6 Å resolution. The crystal belonged to the orthorhombic space group P2(1)2(1)2(1), with two protein molecules in an asymmetric unit.

The crystal structure of alanine racemase from Oenococcus oeni has been determined at 1.7 Å resolution using the single-wavelength anomalous dispersion (SAD) method and selenium-labelled protein. The protein exists as a symmetric dimer in the crystal, with both protomers contributing to the two active sites. Pyridoxal 5'-phosphate, a cofactor, is bound to each monomer and forms a Schiff base with Lys39. Structural comparison of alanine racemase from O. oeni (Alr) with homologous family members revealed similar domain organization and cofactor binding.

Bacillus anthracis, the causative agent of anthrax, has been targeted by the Oxford Protein Production Facility to validate high-throughput protocols within the Structural Proteomics in Europe project. As part of this work, the structures of an alanine racemase (BA0252) in the presence and absence of the inhibitor (R)-1-aminoethylphosphonic acid (L-Ala-P) have determined by X-ray crystallography to resolutions of 2.1 and 1.47 A, respectively. Difficulties in crystallizing this protein were overcome by the use of reductive methylation. Alanine racemase has attracted much interest as a possible target for anti-anthrax drugs: not only is D-alanine a vital component of the bacterial cell wall, but recent studies also indicate that alanine racemase, which is accessible in the exosporium, plays a key role in inhibition of germination in B. anthracis. These structures confirm the binding mode of L-Ala-P but suggest an unexpected mechanism of inhibition of alanine racemase by this compound and could provide a basis for the design of improved alanine racemase inhibitors with potential as anti-anthrax therapies.