title: Conformational analysis of human dihydrofolate reductase inhibitor complexes: crystal structure determination of wild type and F31 mutant binary and ternary inhibitor complexes.
abstract: These structural studies reveal unusual intermolecular interactions for the binding of inhibitors and cofactor in ternary complexes with both wild type and F31 mutant recombinant human DHFR and show that these inhibitors have flexibility in occupying the active site. These studies also possibly indicate the first structural data for a ternary complex with a folate inhibitor and a polyglutamate side chain. However, further refinement of this data is necessary before this can be confirmed. In contrast to the ternary complexes of folate and MTX, the lipophilic antifolate PTX binds with its methoxybenzoyl ring oriented toward the cofactor nicotinamide ring, while that of TMQ it is bound closer to the Phe-31 position. Furthermore, the nicotinamide ring makes a close contact to the N10 amine of TMQ, significantly different from its binding site interactions in MTX complexes. These data also reveal that the conserved contacts between the cofactor carboxyamide with the enzyme backbone residues Ala-9 and Ile-16 are dictated by the enzyme and that changes in the orientation of the structural elements requires only subtle changes in the secondary structural units in which they are contained. Therefore, only by careful analysis of a series of enzyme complexes can the mechanisms of binding action be delineated.
authors.affiliation: Medical Foundation of Buffalo, NY 14203.
authors.forename: V
authors.initials: V
authors.lastname: Cody
authors.forename: A
authors.initials: A
authors.lastname: Wojtczak
authors.forename: T I
authors.initials: TI
authors.lastname: Kalman
authors.forename: J H
authors.initials: JH
authors.lastname: Friesheim
authors.forename: R L
authors.initials: RL
authors.lastname: Blakley
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray / Q000379:methods; D005493:Folic Acid Antagonists / Q000378:metabolism*; D006801:Humans; D008727:Methotrexate / Q000031:analogs & derivatives / Q000378:metabolism; D008958:Models, Molecular; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry* / Q000235:genetics
chemical_list: D005493:Folic Acid Antagonists; D011994:Recombinant Proteins; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate