Davidson VL. Probing mechanisms of catalysis and electron transfer by methylamine dehydrogenase by site-directed mutagenesis of alpha Phe55.
BIOCHIMICA ET BIOPHYSICA ACTA 2003;
1647:230-3. [PMID:
12686138 DOI:
10.1016/s1570-9639(03)00056-6]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
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.
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