title: Structures of human dihydroorotate dehydrogenase in complex with antiproliferative agents.
abstract: BACKGROUND
  Dihydroorotate dehydrogenase (DHODH) catalyzes the fourth committed step in the de novo biosynthesis of pyrimidines. As rapidly proliferating human T cells have an exceptional requirement for de novo pyrimidine biosynthesis, small molecule DHODH inhibitors constitute an attractive therapeutic approach to autoimmune diseases, immunosuppression, and cancer. Neither the structure of human DHODH nor any member of its family was known.
  
  
  RESULTS
  The high-resolution crystal structures of human DHODH in complex with two different inhibitors have been solved. The initial set of phases was obtained using multiwavelength anomalous diffraction phasing with selenomethionine-containing DHODH. The structures have been refined to crystallographic R factors of 16.8% and 16.2% at resolutions of 1. 6 A and 1.8 A for inhibitors related to brequinar and leflunomide, respectively.
  
  
  CONCLUSIONS
  Human DHODH has two domains: an alpha/beta-barrel domain containing the active site and an alpha-helical domain that forms the opening of a tunnel leading to the active site. Both inhibitors share a common binding site in this tunnel, and differences in the binding region govern drug sensitivity or resistance. The active site of human DHODH is generally similar to that of the previously reported bacterial active site. The greatest differences are that the catalytic base removing the proton from dihydroorotate is a serine rather than a cysteine, and that packing of the flavin mononucleotide in its binding site is tighter.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
authors.forename: S
authors.initials: S
authors.lastname: Liu
authors.forename: E A
authors.initials: EA
authors.lastname: Neidhardt
authors.forename: T H
authors.initials: TH
authors.lastname: Grossman
authors.forename: T
authors.initials: T
authors.lastname: Ocain
authors.forename: J
authors.initials: J
authors.lastname: Clardy
mesh_terms: D000595:Amino Acid Sequence; D000814:Aniline Compounds / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D001713:Biphenyl Compounds / Q000737:chemistry; D020134:Catalytic Domain; D003437:Crotonates; D018360:Crystallography, X-Ray; D000090722:Dihydroorotate Dehydrogenase; D006131:Growth Inhibitors / Q000737:chemistry*; D006801:Humans; D006885:Hydroxybutyrates / Q000737:chemistry; D007555:Isoxazoles / Q000737:chemistry; D000077339:Leflunomide; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009570:Nitriles; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D014052:Toluidines; D011798:Quinaldines
chemical_list: D000814:Aniline Compounds; D001713:Biphenyl Compounds; D003437:Crotonates; D000090722:Dihydroorotate Dehydrogenase; D006131:Growth Inhibitors; D006885:Hydroxybutyrates; D007555:Isoxazoles; D000077339:Leflunomide; D046911:Macromolecular Substances; D009570:Nitriles; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D014052:Toluidines; C527525:teriflunomide; C046943:brequinar; D011798:Quinaldines