Monoamine oxidase B (MAO B) is a mitochondrial outermembrane flavoenzyme that is a well-known target for antidepressant and neuroprotective drugs. We determined the structure of the human enzyme to 3 A resolution. The enzyme binds to the membrane through a C-terminal transmembrane helix and apolar loops located at various positions in the sequence. The electron density shows that pargyline, an analog of the clinically used MAO B inhibitor, deprenyl, binds covalently to the flavin N5 atom. The active site of MAO B consists of a 420 A(3)-hydrophobic substrate cavity interconnected to an entrance cavity of 290 A(3). The recognition site for the substrate amino group is an aromatic cage formed by Tyr 398 and Tyr 435. The structure provides a framework for probing the catalytic mechanism, understanding the differences between the B- and A-monoamine oxidase isoforms and designing specific inhibitors.

Many biochemical processes exploit the extraordinary versatility of flavoenzymes and their flavin cofactors. Flavoproteins are now known to have a variety of folding topologies but a careful examination of their structures suggests that there are recurrent features in their catalytic apparatus. The flavoenzymes that catalyse dehydrogenation reactions share a few invariant features in the hydrogen-bond interactions between their protein and flavin constituents. Similarly, the positioning of the reactive part of the substrate with respect to the cofactor is generally conserved. Modulation of substrate and cofactor reactivity and exact positioning of the substrate are key elements in the mode of action of these enzymes.

The three-dimensional structure of recombinant human monoamine oxidase A (hMAO A) as its clorgyline-inhibited adduct is described. Although the chain-fold of hMAO A is similar to that of rat MAO A and human MAO B (hMAO B), hMAO A is unique in that it crystallizes as a monomer and exhibits the solution hydrodynamic behavior of a monomeric form rather than the dimeric form of hMAO B and rat MAO A. hMAO A's active site consists of a single hydrophobic cavity of Ϸ550 Å 3 , which is smaller than that determined from the structure of deprenyl-inhibited hMAO B (Ϸ700 Å 3 ) but larger than that of rat MAO A (Ϸ450 Å 3 ). An important component of the active site structure of hMAO A is the loop conformation of residues 210 -216, which differs from that of hMAO B and rat MAO A. The origin of this structural alteration is suggested to result from long-range interactions in the monomeric form of the enzyme. In addition to serving as a basis for the development of hMAO A specific inhibitors, these data support the proposal that hMAO A involves a change from the dimeric to the monomeric form through a Glu-151 3 Lys mutation that is specific flavin ͉ neurotransmitter ͉ membrane protein ͉ antidepressant target H uman monoamine oxidase A (hMAO A) is an outer mitochondrial membrane-bound flavoenzyme that catalyzes the oxidation of the neurotransmitters serotonin, dopamine, and norepinephrine. Recent studies have demonstrated that a deficiency or low level of expression of this enzyme results in a phenotype of aggressive behavior (1, 2). The elucidation of the 3D structures of human MAO B (hMAO B) (3, 4) (72% sequence identity with hMAO A) and of rat MAO A (rMAO A) (5) (92% sequence identity with hMAO A with no insertions or deletions) has provided insights into the structure and mechanism of these pharmacologically important enzymes. There are several functional properties of hMAO A that differentiate it from rMAO A, despite their high level of sequence identity. hMAO A has been shown to exhibit a 10-fold lower affinity (IC 50 ) than rMAO A for the specific irreversible inhibitor clorgyline (6). Comparisons of the influence of a Phe-208 3 Ile mutation on MAO A from human (7) and rat (8) also show differential effects on activities and sensitivities to irreversible inhibition. Functional differences between hMAO A and rMAO A have been implicated in comparison with their respective sensitivities to phentermine inhibition (9). These differences in properties between hMAO A and rMAO A suggest structural differences exist for these two enzymes.With the development of a high-level expression system for hMAO A in our laboratory (10) and successes with the structural elucidation of hMAO B (3, 4), a collaborative program was established to elucidate the structure of hMAO A by x-ray crystallography. Here, we report the structures of two hMAO A crystal forms and demonstrate structural differences between hMAO A and rMAO A as well as hMAO B. Our data indicate that the considerable literature on MAO A-inhibitor development by using rat models m...

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-Å 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.

Structures of human monoamine oxidase B (MAO B) in complex with safinamide and two coumarin derivatives, all sharing a common benzyloxy substituent, were determined by X-ray crystallography. These compounds competitively inhibit MAO B with Ki values in the 0.1-0.5 microM range that are 30-700-fold lower than those observed with MAO A. The inhibitors bind noncovalently to MAO B, occupying both the entrance and the substrate cavities and showing a similarly oriented benzyloxy substituent.

LSD1 and LSD2 histone demethylases are implicated in a number of physiological and pathological processes, ranging from tumorigenesis to herpes virus infection. A comprehensive structural, biochemical, and cellular study is presented here to probe the potential of these enzymes for epigenetic therapies. This approach employs tranylcypromine as a chemical scaffold for the design of novel demethylase inhibitors. This drug is a clinically validated antidepressant known to target monoamine oxidases A and B. These two flavoenzymes are structurally related to LSD1 and LSD2. Mechanistic and crystallographic studies of tranylcypromine inhibition reveal a lack of selectivity and differing covalent modifications of the FAD cofactor depending on the enantiomeric form. These findings are pharmacologically relevant, since tranylcypromine is currently administered as a racemic mixture. A large set of tranylcypromine analogues were synthesized and screened for inhibitory activities. We found that the common evolutionary origin of LSD and MAO enzymes, despite their unrelated functions and substrate specificities, is reflected in related ligand-binding properties. A few compounds with partial enzyme selectivity were identified. The biological activity of one of these new inhibitors was evaluated with a cellular model of acute promyelocytic leukemia chosen since its pathogenesis includes aberrant activities of several chromatin modifiers. Marked effects on cell differentiation and an unprecedented synergistic activity with antileukemia drugs were observed. These data demonstrate that these LSD1/2 inhibitors are of potential relevance for the treatment of promyelocytic leukemia and, more generally, as tools to alter chromatin state with promise of a block of tumor progression.

Over time, organisms have evolved strategies to cope with the abundance of dioxygen on Earth. Oxygen-utilizing enzymes tightly control the reactions involving O mostly by modulating the reactivity of their cofactors. Flavins are extremely versatile cofactors that are capable of undergoing redox reactions by accepting either one electron or two electrons, alternating between the oxidized and the reduced states. The physical and chemical principles of flavin-based chemistry have been investigated widely. In the following pages we summarize the state of the art on a key area of research in flavin enzymology: the molecular basis for the activation of O by flavin-dependent oxidases and monooxygenases. In general terms, oxidases use O as an electron acceptor to produce HO, while monooxygenases activate O by forming a flavin intermediate and insert an oxygen atom into the substrate. First, we analyze how O reaches the flavin cofactor embedded in the protein matrix through dedicated access pathways. Then we approach O activation from the perspective of the monooxygenases, their preferred intermediate, the C(4a)-(hydro)peroxyflavin, and the cases in which other intermediates have been described. Finally, we focus on understanding how the architectures developed in the active sites of oxidases promote O activation and which other factors operate in its reactivity.

Histone demethylase LSD1 regulates transcription by demethylating Lys 4 of histone H3. The crystal structure of the enzyme in complex with CoREST and a substrate-like peptide inhibitor highlights an intricate network of interactions and a folded conformation of the bound peptide. The core of the peptide structure is formed by Arg 2 , Gln 5 , and Ser 10 , which are engaged in specific intramolecular H-bonds. Several charged side chains on the surface of the substrate-binding pocket establish electrostatic interactions with the peptide. The three-dimensional structure predicts that methylated Lys 4 binds in a solvent inaccessible position in front of the flavin cofactor. This geometry is fully consistent with the demethylation reaction being catalyzed through a flavin-mediated oxidation of the substrate amino-methyl group. These features dictate the exquisite substrate specificity of LSD1 and provide a structural framework to explain the fine tuning of its catalytic activity and the active role of CoREST in substrate recognition.Lysine methylation is among the most well characterized histone modifications, and its existence has been known since the early days of chromatin research (1, 2). This type of epigenetic mark provides a huge potential for functional responses in that it can occur in different forms (mono-, di-, and tri-methylation) and on different histone sites, each having a specific physiological meaning. Histone methylation has been long thought to be a low turnover epigenetic mark, but the recent discovery of histone demethylases (3, 4) has challenged this view by demonstrating that histone lysine methylation can be actively and dynamically regulated. Two classes of histone demethylases have been uncovered; the enzymes of the JmjC family use iron as cofactor, whereas lysine-specific demethylase 1 (LSD1) 4 employs FAD as the prosthetic group (5).LSD1 catalyzes the oxidative demethylation of mono-and dimethyl Lys 4 of histone H3, generating hydrogen peroxide and formaldehyde (3, 4). The enzyme is implicated as a key component of distinct co-activator and co-repressor complexes in a surprisingly wide range of cellular processes where it participates in the dynamic transition of transcriptional programs (6). Its catalytic activity is finely tuned by the epigenetic marks present on the H3 N-terminal tail (7) and by other protein partners, such as CoREST, that form a stable complex with the enzyme (8, 9). The three-dimensional structure of LSD1 in its native state (10, 11) and in complex with the LSD1-binding domain of CoREST (12) have revealed that the catalytic center is located in the core of the enzyme main body. A protruding tower domain consisting of two remarkably long helices forms the docking site for the co-repressor protein (Fig. 1A).Here, we describe the structural analysis of LSD1-CoREST bound to a 21-amino acid H3 peptide in which pLys 4 ("p" is for peptide) is mutated to Met. The structural analysis illuminates the molecular properties that enable LSD1 to function as a key transcriptional reg...