title: Crystal structure of diaminopelargonic acid synthase: evolutionary relationships between pyridoxal-5'-phosphate-dependent enzymes.
abstract: The three-dimensional structure of diaminopelargonic acid synthase, a vitamin B6-dependent enzyme in the pathway of the biosynthesis of biotin, has been determined to 1.8 A resolution by X-ray crystallography. The structure was solved by multi-wavelength anomalous diffraction techniques using a crystal derivatized with mercury ions. The protein model has been refined to a crystallographic R -value of 17.5% (R -free 22.6%). Each enzyme subunit consists of two domains, a large domain (residues 50-329) containing a seven-stranded predominantly parallel beta-sheet, surrounded by alpha-helices, and a small domain comprising residues 1-49 and 330-429. Two subunits, related by a non-crystallographic dyad in the crystals, form the homodimeric molecule, which contains two equal active sites. Pyridoxal-5'-phosphate is bound in a cleft formed by both domains of one subunit and the large domain of the second subunit. The cofactor is anchored to the enzyme by a covalent linkage to the side-chain of the invariant residue Lys274. The phosphate group interacts with main-chain nitrogen atoms and the side-chain of Ser113, located at the N terminus of an alpha-helix. The pyridine nitrogen forms a hydrogen bond to the side-chain of the invariant residue Asp245. Electron density corresponding to a metal ion, most likely Na(+), was found in a tight turn at the surface of the enzyme. Structure analysis reveals that diaminopelargonic acid synthase belongs to the family of vitamin B6-dependent aminotransferases with the same fold as originally observed in aspartate aminotransferase. A multiple structure alignment of enzymes in this family indicated that they form at least six different subclasses. Striking differences in the fold of the N-terminal part of the polypeptide chain are one of the hallmarks of these subclasses. Diaminopelargonic acid synthase is a member of the aminotransferase subclass III. From the structure of the non-productive complex of the holoenzyme with the substrate 7-keto-8-aminopelargonic acid the location of the active site and residues involved in substrate binding have been identified.
authors.affiliation: Division of Structural Biology Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Doktorsringen 9, Stockholm, S-171 77, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Käck
authors.forename: J
authors.initials: J
authors.lastname: Sandmark
authors.forename: K
authors.initials: K
authors.lastname: Gibson
authors.forename: G
authors.initials: G
authors.lastname: Schneider
authors.forename: Y
authors.initials: Y
authors.lastname: Lindqvist
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D011732:Pyridoxal Phosphate / Q000378:metabolism; D055672:Static Electricity; D013379:Substrate Specificity; D000637:Transaminases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D011732:Pyridoxal Phosphate; C020029:7,8-diaminopelargonic acid aminotransferase; D000637:Transaminases