Potentiation of ligand binding through cooperative effects in monoamine oxidase B.
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.
Bonivento
Daniele
D
Department of Genetics and Microbiology, University of Pavia, I-27100 Pavia PV, Italy.
Milczek
Erika M
EM
McDonald
G Reid
GR
Binda
Claudia
C
Holt
Andrew
A
Edmondson
Dale E
DE
Mattevi
Andrea
A
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
D001572:Benzofurans; D007093:Imidazoles; D008996:Monoamine Oxidase Inhibitors; D011994:Recombinant Proteins; D014191:Tranylcypromine; C103723:2-(2-benzofuranyl)-2-imidazoline; D008995:Monoamine Oxidase