Insights into the mode of inhibition of human mitochondrial monoamine oxidase B from high-resolution crystal structures.
Monoamine oxidase B (MAO-B) is an outer mitochondrial membrane-bound enzyme that catalyzes the oxidative deamination of arylalkylamine neurotransmitters and has been a target for a number of clinically used drug inhibitors. The 1.7-A structure of the reversible isatin-MAO-B complex has been determined; it forms a basis for the interpretation of the enzyme's structure when bound to either reversible or irreversible inhibitors. 1,4-Diphenyl-2-butene is found to be a reversible MAO-B inhibitor, which occupies both the entrance and substrate cavity space in the enzyme. Comparison of these two structures identifies Ile-199 as a "gate" between the two cavities. Rotation of the side chain allows for either separation or fusion of the two cavities. Inhibition of the enzyme with N-(2-aminoethyl)-p-chlorobenzamide results in the formation of a covalent N(5) flavin adduct with the phenyl ring of the inhibitor occupying a position in the catalytic site overlapping that of isatin. Inhibition of MAO-B with the clinically used trans-2-phenylcyclopropylamine results in the formation of a covalent C(4a) flavin adduct with an opened cyclopropyl ring and the phenyl ring in a parallel orientation to the flavin. The peptide bond between the flavin-substituted Cys-397 and Tyr-398 is in a cis conformation, which allows the proper orientation of the phenolic ring of Tyr-398 in the active site. The flavin ring exists in a twisted nonplanar conformation, which is observed in the oxidized form as well as in both the N(5) and the C(4a) adducts. An immobile water molecule is H-bonded to Lys-296 and to the N(5) of the flavin as observed in other flavin-dependent amine oxidases. The active site cavities are highly apolar; however, hydrophilic areas exist near the flavin and direct the amine moiety of the substrate for binding and catalysis. Small conformational changes are observed on comparison of the different inhibitor-enzyme complexes. Future MAO-B drug design will need to consider "induced fit" contributions as an element in ligand-enzyme interactions.
Binda
Claudia
C
Department of Genetics and Microbiology, University of Pavia, Via Abbiategrasso, 27100 Pavia, Italy.
Li
Min
M
Hubalek
Frantisek
F
Restelli
Nadia
N
Edmondson
Dale E
DE
Mattevi
Andrea
A
D020134:Catalytic Domain; D003067:Coenzymes / Q000737:chemistry; D018360:Crystallography, X-Ray; D005415:Flavins / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D007510:Isatin / Q000737:chemistry / Q000494:pharmacology; D008928:Mitochondria / Q000201:enzymology; D008958:Models, Molecular; D008995:Monoamine Oxidase / Q000737:chemistry*; D008996:Monoamine Oxidase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D011487:Protein Conformation; D055672:Static Electricity
D003067:Coenzymes; D005415:Flavins; D008996:Monoamine Oxidase Inhibitors; D007510:Isatin; D008995:Monoamine Oxidase