title: Potentiation of ligand binding through cooperative effects in monoamine oxidase B.
abstract: Crystallographic and biochemical studies have been employed to identify the binding site and mechanism for potentiation of imidazoline binding in human monoamine oxidase B (MAO B). 2-(2-Benzofuranyl)-2-imidazoline (2-BFI) inhibits recombinant human MAO B with a K(i) of 8.3 ± 0.6 μM, whereas tranylcypromine-inhibited MAO B binds 2-BFI with a K(d) of 9 ± 2 nM, representing an increase in binding energy Δ(ΔG) of -3.9 kcal/mol. Crystal structures show the imidazoline ligand bound in a site that is distinct from the substrate-binding cavity. Contributions to account for the increase in binding affinity upon tranylcypromine inhibition include a conformational change in the side chain of Gln(206) and a "closed conformation" of the side chain of Ile(199), forming a hydrophobic "sandwich" with the side chain of Ile(316) on each face of the benzofuran ring of 2-BFI. Data with the I199A mutant of human MAO B and failure to observe a similar binding potentiation with rat MAO B, where Ile(316) is replaced with a Val residue, support an allosteric mechanism where the increased binding affinity of 2-BFI results from a cooperative increase in H-bond strength through formation of a more hydrophobic milieu. These insights should prove valuable in the design of high affinity and specific reversible MAO B inhibitors.
authors.affiliation: Department of Genetics and Microbiology, University of Pavia, I-27100 Pavia PV, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Bonivento
authors.forename: Erika M
authors.initials: EM
authors.lastname: Milczek
authors.forename: G Reid
authors.initials: GR
authors.lastname: McDonald
authors.forename: Claudia
authors.initials: C
authors.lastname: Binda
authors.forename: Andrew
authors.initials: A
authors.lastname: Holt
authors.forename: Dale E
authors.initials: DE
authors.lastname: Edmondson
authors.forename: Andrea
authors.initials: A
authors.lastname: Mattevi
mesh_terms: D001572:Benzofurans / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D018360:Crystallography, X-Ray; D006801:Humans; D007093:Imidazoles / Q000378:metabolism*; D008995:Monoamine Oxidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014191:Tranylcypromine / Q000494:pharmacology
chemical_list: D001572:Benzofurans; D007093:Imidazoles; D008996:Monoamine Oxidase Inhibitors; D011994:Recombinant Proteins; D014191:Tranylcypromine; C103723:2-(2-benzofuranyl)-2-imidazoline; D008995:Monoamine Oxidase