title: The 1.8 A crystal structure of catechol 1,2-dioxygenase reveals a novel hydrophobic helical zipper as a subunit linker.
abstract: BACKGROUND
  Intradiol dioxygenases catalyze the critical ring-cleavage step in the conversion of catecholate derivatives to citric acid cycle intermediates. Catechol 1,2-dioxygenases (1, 2-CTDs) have a rudimentary design structure - a homodimer with one catalytic non-heme ferric ion per monomer, that is (alphaFe(3+))(2). This is in contrast to the archetypical intradiol dioxygenase protocatechuate 3,4-dioxygenase (3,4-PCD), which forms more diverse oligomers, such as (alphabetaFe(3+))(2-12).
  
  
  RESULTS
  The crystal structure of 1,2-CTD from Acinetobacter sp. ADP1 (Ac 1,2-CTD) was solved by single isomorphous replacement and refined to 2.0 A resolution. The structures of the enzyme complexed with catechol and 4-methylcatechol were also determined at resolutions of 1.9 A and 1.8 A, respectively. While the characteristics of the iron ligands are similar, Ac 1,2-CTD differs from 3,4-PCDs in that only one subunit is used to fashion each active-site cavity. In addition, a novel 'helical zipper', consisting of five N-terminal helices from each subunit, forms the molecular dimer axis. Two phospholipids were unexpectedly found to bind within an 8 x 35 A hydrophobic tunnel along this axis.
  
  
  CONCLUSIONS
  The helical zipper domain of Ac 1, 2-CTD has no equivalent in other proteins of known structure. Sequence analysis suggests the domain is a common motif in all members of the 1,2-CTD family. Complexes with catechol and 4-methylcatechol are the highest resolution complex structures to date of an intradiol dioxygenase. Furthermore, they confirm several observations seen in 3,4-PCDs, including ligand displacement upon binding exogenous ligands. The structures presented here are the first of a new family of intradiol dioxygenases.
authors.affiliation: The department of Biochemistry, Molecular Biology and Biophysics, Center for Metals in Biocatalysis, University of Minnesota Medical School, Minneapolis, MN 55455-0347, USA.
authors.forename: M W
authors.initials: MW
authors.lastname: Vetting
authors.forename: D H
authors.initials: DH
authors.lastname: Ohlendorf
mesh_terms: D000150:Acinetobacter / Q000201:enzymology; D001665:Binding Sites; D020134:Catalytic Domain; D050548:Catechol 1,2-Dioxygenase; D018360:Crystallography, X-Ray; D049308:Dioxygenases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008627:Mercuric Chloride / Q000494:pharmacology; D008958:Models, Molecular; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D011487:Protein Conformation; D011520:Protocatechuate-3,4-Dioxygenase / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D010743:Phospholipids; D008627:Mercuric Chloride; D010105:Oxygenases; D049308:Dioxygenases; D050548:Catechol 1,2-Dioxygenase; D011520:Protocatechuate-3,4-Dioxygenase