The ‘gating’ residues Ile199 and Tyr326 in human monoamine oxidase B function in substrate and inhibitor recognition

Abstract

Summary The major structural difference between human monoamine oxidases A (MAO A) and B (MAO B) is that MAO A has a monopartite substrate cavity of ~550 Å3 volume and MAO B contains a dipartite cavity structure with volumes of ~290 Å3 (entrance cavity) and ~400 Å3 (substrate cavity). Ile199 and Tyr326 side chains separate these two cavities in MAO B. To probe the function of these gating residues, Ile199Ala and Ile199Ala Tyr326Ala mutant forms of MAO B were investigated. Structural data on the Ile199Ala MAO B mutant show no alterations in active site geometries compared to WT enzyme while the Ile199Ala-Tyr326Ala MAO B mutant exhibits alterations in residues 100–103 which are part of the loop gating the entrance to the active site. Both mutant enzymes exhibit catalytic properties with increased amine KM but unaltered kcat values. The altered KM values on mutation are attributed to the influence of the cavity structure in the binding and subsequent deprotonation of the amine substrate. Both mutant enzymes exhibit weaker binding affinities relative to WT enzyme for small reversible inhibitors. Ile199Ala MAO B exhibits an increase in binding affinity for reversible MAO B specific inhibitors which bridge both cavities. The Ile199Ala-Tyr326Ala double mutant exhibits inhibitor binding properties more similar to those of MAO A than to MAO B. These results demonstrate the bipartite cavity structure in MAO B plays an important role in substrate and inhibitor recognition to distinguish its specificities from those of MAO A and provides insights into specific reversible inhibitor design for these membrane-bound enzymes.

Synthesis of a series of unsaturated ketone derivatives as selective and reversible monoamine oxidase inhibitors

“…4, the binding pose of 10b in the substrate binding site of hMAO-A was different from hMAO-B because of the difference of structural conformation within substrate binding cavity. Leu171, Ile199 and Tyr326 residues of hMAO-B are gatekeeper residues 24,25 and corresponding residues in MAO-A are Ile180, Phe208 and Ile335 which might affect binding selectivity of 10b. Therefore, molecular docking studies suggested that excellent activity and selectivity of 10b are probably relied on the key interactions with the Leu171, Ile199 and Tyr326 residues within substrate binding pocket of hMAO-B.…”

What a Difference a Methyl Group Makes: The Selectivity of Monoamine Oxidase B Towards Histamine and N‐Methylhistamine

“…In contrast, NMH always forms hydrophobic contacts with at least one of those residues, and frequently with all three ( Figure S3 in the Supporting Information). [27] Interestingly,I le199 is conserved in all known MAO Bs equences except bovine MAO B, which has Phe in this positiont hat is, in turn, ac onserved residue in the analogous positioni nM AO A. [27] Interestingly,I le199 is conserved in all known MAO Bs equences except bovine MAO B, which has Phe in this positiont hat is, in turn, ac onserved residue in the analogous positioni nM AO A.…”

Computational Drug Target Screening through Protein Interaction Profiles

“…Both compounds were found to interact preferentially with residues Leu171, Ile199, Gln206, Tyr326 and Tyr398. The important role of the cited residues in ligand binding, such as Ile199 and Tyr326, was previously reported through molecular docking and site-directed mutagenesis studies2733.…”