Mutagenic probes of the role of Ser209 on the cavity shaping loop of human monoamine oxidase A.
The available literature implicating human monoamine oxidase A (MAO A) in apoptotic processes reports levels of MAO A protein that do not correlate with activity, suggesting that unknown mechanisms may be involved in the regulation of catalytic function. Bioinformatic analysis suggests Ser209 as a possible phosphorylation site that may be relevant to catalytic function because it is adjacent to a six-residue loop termed the 'cavity shaping loop' from structural data. To probe the functional role of this site, MAO A Ser209Ala and Ser209Glu mutants were created and investigated. In its membrane-bound form, the MAO A Ser209Glu phosphorylation mimic exhibits catalytic and inhibitor binding properties similar to those of wild-type MAO A. Solubilization in detergent solution and purification of the Ser209Glu mutant results in considerable decreases in these functional parameters. By contrast, the MAO A Ser209Ala mutant exhibits similar catalytic properties to those of wild-type enzyme when purified. Compared to purified wild-type and Ser209Ala MAO A proteins, the Ser209Glu MAO A mutant shows significant differences in covalent flavin fluorescence yield, CD spectra and thermal stability. These structural differences in the purified MAO A Ser209Glu mutant are not exhibited in quantitative structure-activity relationship patterns using a series of para-substituted benzylamine analogs similar to the wild-type enzyme. These data suggest that Ser209 in MAO A does not appear to be the putative phosphorylation site for regulation of MAO A activity and demonstrate that the membrane environment plays a significant role in stabilizing the structure of MAO A and its mutant forms.
Wang
Jin
J
Department of Biochemistry, Emory University, Atlanta, GA 30322, USA.
Harris
Johnny
J
Mousseau
Darrell D
DD
Edmondson
Dale E
DE
D002384:Catalysis; D005415:Flavins; D005453:Fluorescence; D006801:Humans; D008995:Monoamine Oxidase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D055550:Protein Stability; D012694:Serine / Q000378:metabolism*; D013329:Structure-Activity Relationship
D005415:Flavins; D012694:Serine; D008995:Monoamine Oxidase