title: Structural symmetry: the three-dimensional structure of Haemophilus influenzae diaminopimelate epimerase.
abstract: The Haemophilus influenzae diaminopimelate epimerase was cloned, expressed, purified, and crystallized in the C2221 space group (a = 102.1 A, b = 115.4 A, c = 66.3 A, alpha = beta = gamma = 90 degrees). The three-dimensional structure was solved to 2.7 A using a single Pt derivative and the Se-Met-substituted enzyme to a conventional R factor of 19.0% (Rfree = 24.2%). The 274 amino acid enzyme consists of two structurally homologous domains, each containing eight beta-strands and two alpha-helices. Diaminopimelate epimerase is a representative of the PLP-independent amino acid racemases, for which no structure has yet been determined and substantial evidence exists supporting the role of two cysteine residues as the catalytic acid and base. Cys73 of the amino terminal domain is found in disulfide linkage, at the domain interface, with Cys217 of the carboxy terminal domain, and we suggest that these two cysteine residues in the reduced, active enzyme function as the acid and base in the mechanism.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: M
authors.initials: M
authors.lastname: Cirilli
authors.forename: R
authors.initials: R
authors.lastname: Zheng
authors.forename: G
authors.initials: G
authors.lastname: Scapin
authors.forename: J S
authors.initials: JS
authors.lastname: Blanchard
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D003553:Cystine / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D006193:Haemophilus influenzae / Q000201:enzymology*; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004220:Disulfides; D003553:Cystine; D000591:Amino Acid Isomerases; C042032:diaminopimelate epimerase