title: Crystal structure at 1.45 A resolution of alanine racemase from a pathogenic bacterium, Pseudomonas aeruginosa, contains both internal and external aldimine forms.
abstract: The structure of the catabolic alanine racemase, DadX, from the pathogenic bacterium Pseudomonas aeruginosa, reported here at 1.45 A resolution, is a dimer in which each monomer is comprised of two domains, an eight-stranded alpha/beta barrel containing the PLP cofactor and a second domain primarily composed of beta-strands. The geometry of each domain is very similar to that of Bacillus stearothermophilus alanine racemase, but the rotation between domains differs by about 15 degrees. This change does not alter the structure of the active site in which almost all residues superimpose well with a low rms difference of 0.86 A. Unexpectedly, the active site of DadX contains a guest substrate that is located where acetate and propionate have been observed in the Bacillus structures. It is modeled as d-lysine and oriented such that its terminal NZ atom makes a covalent bond with C4' of PLP. Since the internal aldimine bond between the protein lysine, Lys33, and C4' of PLP is also unambiguously observed, there appears to be an equilibrium between both internally and externally reacted forms. The PLP cofactor adopts two partially occupied conformational states that resemble previously reported internal and external aldimine complexes.
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204, USA.
authors.forename: Pierre
authors.initials: P
authors.lastname: LeMagueres
authors.forename: Hookang
authors.initials: H
authors.lastname: Im
authors.forename: Anna
authors.initials: A
authors.lastname: Dvorak
authors.forename: Ulrich
authors.initials: U
authors.lastname: Strych
authors.forename: Michael
authors.initials: M
authors.lastname: Benedik
authors.forename: Kurt L
authors.initials: KL
authors.lastname: Krause
mesh_terms: D000411:Alanine Racemase / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D006860:Hydrogen Bonding; D007097:Imines / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D011732:Pyridoxal Phosphate / Q000737:chemistry; D016415:Sequence Alignment
chemical_list: D007097:Imines; D010446:Peptide Fragments; D011732:Pyridoxal Phosphate; D000411:Alanine Racemase