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ABSTRACT: Structural studies on recombinant human monoamine oxidase A (hMAO-A) provides interesting insights on comparison with that determined for human MAO-B (hMAO-B) as well as comparison with that previously published for rat MAO-A. The active site cavity of hMAO-A is monopartite (as with rat MAO-A) while hMAO-B is a bipartite cavity. hMAO-A crystallizes as a monomeric form, in contrast to the dimeric forms exhibited by hMAO-B and rat MAO-A. All of the known MAO structures show nearly identical geometries around the covalent FAD sites. Differences in active site cavity structures occur away from the FAD site through conformational alterations (MAO-A's) and by changes in amino acid residues (hMAO-A and hMAO-B). Differences observed between human and rat MAO-A's raise questions regarding the appropriateness of the rat model in the development of MAO-A specific inhibitors as drugs for eventual human use.
Acta Neurovegetativa 02/2007; 114(6):703-5. · 2.73 Impact Factor
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ABSTRACT: Monoamine oxidase B (MAO-B) is an outer mitochondrial membrane-bound flavoenzyme that is a well-known target for antidepressant and neuroprotective drugs. The 3A resolution structure of recombinant human MAO-B originally determined was of the enzyme complexed with pargyline, an irreversible inhibitor covalently bound to the N5 atom of the flavin coenzyme. The crystal structure shows that the enzyme is dimeric. Each monomer binds to the membrane via a C-terminal transmembrane helix and by apolar loops located at various positions in the sequence. Substrate binding to the enzyme involves negotiating a loop covering a 290A3 entrance apolar cavity before reaching an apolar 420A3 substrate cavity where the flavin coenzyme is located. The 1.7A isatin-MAO-B structure allowed a detailed examination of the enzyme's active site. A novel specific reversible MAO-B inhibitor, which is found as a contaminant in polystyrene plastics (1,4-diphenyl-2-butene), binds in both the entrance and the substrate cavity. Analogous MAO-B-specific inhibitors that bind in a manner traversing both cavities include trans-trans farnesol and chlorostyrylcaffeine. The rotation of the Ile199 side chain to an "open" conformation plays an essential role in this specificity. These results form a molecular basis for the design of new human MAO-B-specific reversible inhibitors.
Neurology 11/2006; 67(7 Suppl 2):S5-7. · 8.31 Impact Factor
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ABSTRACT: Monoamine oxidases A and B (MAO A and MAO B) are mitochondrial outer membrane-bound flavoproteins that catalyze the oxidative deamination of neurotransmitters and biogenic amines. A number of mechanism-based inhibitors (MAOI's) have been developed for clinical use as antidepressants and as neuroprotective drugs. To facilitate the development of more effective and specific inhibitors, a detailed understanding of the structures and catalytic mechanisms of these enzymes is required. The recent development of high level expression systems for producing recombinant human liver MAO A and MAO B in Pichia pastoris has facilitated the determination of the three dimensional crystal structures of MAO B (up to 1.7 angstroms resolution) in complex with different reversible (isatin, 1,4-diphenyl-2-butene) and irreversible inhibitors (pargyline, N-(2-aminoethyl)-p-chlorobenzamide, and trans-2-phenylcyclopropylamine). The binding of substrates or inhibitors to MAO B involves an initial negotiation of a protein loop occurring near the surface of the membrane and two hydrophobic cavities; an "entrance" cavity and an "active site" cavity. These two cavities can either be separate or in a fused state depending on the conformation of the Ile199 side chain, which appears to function as a gate. The amine function of the bound substrate approaches the re face of the bent and "puckered" covalent FAD through an "aromatic cage" formed by two tyrosine residues that are perpendicular to the plane of the flavin ring. No amino acid residues that could function as acids or bases are found near the catalytic site. The existing structural data on MAO B support previous QSAR results and are also supportive of a proposed polar nucleophilic mechanism for MAO A and B catalysis rather than the alternatively proposed single electron transfer mechanism.
Current Medicinal Chemistry 09/2004; 11(15):1983-93. · 4.86 Impact Factor
