title: Three-dimensional structure of iminodisuccinate epimerase defines the fold of the MmgE/PrpD protein family.
abstract: Iminodisuccinate (IDS) epimerase catalyzes the epimerisation of R,R-, S,S- and R,S- iminodisuccinate, one step in the biodegradation of the chelating agent iminodisuccinate by Agrobacterium tumefaciens BY6. The enzyme is a member of the MmgE/PrpD protein family, a diverse and little characterized class of proteins of prokaryotic and eukaryotic origin. IDS epimerase does not show significant overall amino acid sequence similarity to any other protein of known three-dimensional structure. The crystal structure of this novel epimerase has been determined by multi-wavelength diffraction to 1.5 A resolution using selenomethionine-substituted enzyme. In the crystal, the enzyme forms a homo-dimer, and the subunit consists of two domains. The larger domain, not consecutive in sequence and comprising residues Met1-Lys266 and Leu400-Pro446, forms a novel all alpha-helical fold with a central six-helical bundle. The second, smaller domain folds into an alpha+beta domain, related in topology to chorismate mutase by a circular permutation. IDS epimerase is thus not related in three-dimensional structure to other known epimerases. The fold of the IDS epimerase is representative for the whole MmgE/PrpD family. The putative active site is located at the interface between the two domains of the subunit, and is characterized by a positively charged surface, consistent with the binding of a highly negatively charged substrate such as iminodisuccinate. Docking experiments suggest a two-base mechanism for the epimerisation reaction.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 171 77 Stockholm, Sweden.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lohkamp
authors.forename: Bettina
authors.initials: B
authors.lastname: Bäuerle
authors.forename: Paul-Gerhard
authors.initials: PG
authors.lastname: Rieger
authors.forename: Gunter
authors.initials: G
authors.lastname: Schneider
mesh_terms: D016960:Agrobacterium tumefaciens / Q000201:enzymology / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013386:Succinates / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D013386:Succinates; C412825:iminodisuccinic acid; D019998:Racemases and Epimerases; C513549:imidodisuccinate epimerase, Agrobacterium tumefaciens