Probing mechanisms of catalysis and electron transfer by methylamine dehydrogenase by site-directed mutagenesis of alpha Phe55.
Methylamine dehydrogenase (MADH) possesses an alpha(2)beta(2) subunit structure with each smaller beta subunit possessing a tryptophan tryptophylquinone (TTQ) prosthetic group. Phe(55) of the alpha subunit is located where the substrate channel from the enzyme surface opens into the active site. Site-directed mutagenesis studies have revealed several roles for this residue in catalysis and electron transfer (ET) by MADH. Site-directed mutagenesis of either alpha Phe(55) or beta Ile(107) (a residue in the beta subunit which interacts with alpha Phe(55)) converts MADH into enzymes with specificities for long-chain amines, amylamine or propylamine. Mutation of alpha Phe(55) also affects monovalent cation binding to the active site. alpha F55A MADH exhibits an increased K(d) for cation-dependent spectral changes and a decreased K(d) for cation-dependent stimulation of the rate of gated ET from N-quinol MADH to amicyanin. These results demonstrate that alpha Phe(55) is able to directly participate in a wide range of biochemical processes not typically observed for a phenylalanine residue.
Davidson
Victor L
VL
Department of Biochemistry, The University of Mississippi Medical Center, 2500 N. State Street, Jackson, MS 39216-4505, USA. vdavidson@biochem.umsmed.edu
D001665:Binding Sites; D002384:Catalysis; D016297:Mutagenesis, Site-Directed; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000737:chemistry* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D012964:Sodium; C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; D011188:Potassium