Insights into the mode of inhibition of human mitochondrial monoamine oxidase B from high-resolution crystal structures.
Binda, Claudia ; Li, Min ; Hubalek, Frantisek ; et al. ; - ASI Sponsor
Aug - 2003
ISSN : 0027-8424 ;
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type: Conference Proceedings

Abstract
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 enzymes 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.

keywords : Catalytic Domain,Coenzymes,Coenzymes: chemistry,Crystallography,Flavins,Flavins: chemistry,Humans,Isatin,Isatin: chemistry,Isatin: pharmacology,Mitochondria,Mitochondria: enzymology,Models,Molecular,Monoamine Oxidase,Monoamine Oxidase Inhibitors,Monoamine Oxidase Inhibitors: chemistry,Monoamine Oxidase Inhibitors: pharmacology,Monoamine Oxidase: chemistry,Protein Conformation,Static Electricity,X-Ray