title: Crystal structure of Tritrichomonas foetus inosine-5'-monophosphate dehydrogenase and the enzyme-product complex.
abstract: Inosine-5'-monophosphate dehydrogenase (IMPDH) is an attractive drug target for the control of parasitic infections. The enzyme catalyzes the oxidation of inosine monophosphate (IMP) to xanthosine monophosphate (XMP), the committed step in de novo guanosine monophosphate (GMP) biosynthesis. We have determined the crystal structures of IMPDH from the protozoan parasite Tritrichomonas foetus in the apo form at 2.3 A resolution and the enzyme-XMP complex at 2.6 A resolution. Each monomer of this tetrameric enzyme is comprised of two domains, the largest of which includes an eight-stranded parallel beta/alpha-barrel that contains the enzyme active site at the C termini of the barrel beta-strands. A second domain, comprised of residues 102-220, is disordered in the crystal. IMPDH is expected to be active as a tetramer, since the active site cavity is formed by strands from adjacent subunits. An intrasubunit disulfide bond, seen in the crystal structure, may stabilize the protein in a less active form, as high concentrations of reducing agent have been shown to increase enzyme activity. Disorder at the active site suggests that a high degree of flexibility may be inherent in the catalytic function of IMPDH. Unlike IMPDH from other species, the T. foetus enzyme has a single arginine that is largely responsible for coordinating the substrate phosphate in the active site. This structural uniqueness may facilitate structure-based identification and design of compounds that specifically inhibit the parasite enzyme.
authors.affiliation: Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, 94143-0446, USA. frankw@solitude.med.utah.edu
authors.forename: F G
authors.initials: FG
authors.lastname: Whitby
authors.forename: H
authors.initials: H
authors.lastname: Luecke
authors.forename: P
authors.initials: P
authors.lastname: Kuhn
authors.forename: J R
authors.initials: JR
authors.lastname: Somoza
authors.forename: J A
authors.initials: JA
authors.lastname: Huete-Perez
authors.forename: J D
authors.initials: JD
authors.lastname: Phillips
authors.forename: C P
authors.initials: CP
authors.lastname: Hill
authors.forename: R J
authors.initials: RJ
authors.lastname: Fletterick
authors.forename: C C
authors.initials: CC
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D007168:IMP Dehydrogenase / Q000737:chemistry*; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry*; D016835:Tritrichomonas foetus / Q000737:chemistry / Q000201:enzymology*
chemical_list: D015800:Protozoan Proteins; D007168:IMP Dehydrogenase