title: Characterization of osmolyte betaine synthesizing sarcosine dimethylglycine N-methyltransferase from Methanohalophilus portucalensis.
abstract: To overcome the extracellular salt stress, Methanohalophilus portucalensis FDF1(T) synthesizes the compatible solute betaine through the methylation of glycine, sarcosine, and N,N-dimethylglycine. S-adenosylmethionine (AdoMet) is the methyl donor. The enzyme sarcosine dimethylglycine N-methyltransferase (SDMT) of M. portucalensis, that catalyzes the formation of N,N-dimethylglycine and glycine betaine, has been purified and characterized. SDMT, a monomer of 33 kDa with a pI at 5.03, has a narrow substrate specificity limited to using only sarcosine and dimethylglycine as substrates for the methyl transferase reaction. The K(m) values for sarcosine and AdoMet were 2.29 and 0.21 mM, respectively, with a V(max) of 0.83 micromol/mg-min (k(cat) value of 0.44 s(-1)). The K(m) values for dimethylglycine and AdoMet were 3.76 and 0.59 mM, respectively, with a V(max) of 4.88 micromol/mg-min (k(cat) of 2.68 s(-1)). A high concentration of the end product betaine (2.0 M) did not affect the SMT activity, but it slightly inhibited the DMT activity. Both activities were also not affected by potassium or sodium ions in concentrations of 200-1,000 mM. We compared this novel archaeal SDMT enzyme to other similar bacterial transferases as well as to the glycine sarcosine dimethylglycine methyltransferase found also in M. portucalensis.
authors.affiliation: Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan, ROC.
authors.forename: Shih-Ya
authors.initials: SY
authors.lastname: Chen
authors.forename: Mei-Chin
authors.initials: MC
authors.lastname: Lai
authors.forename: Shu-Jung
authors.initials: SJ
authors.lastname: Lai
authors.forename: Yu-Chien
authors.initials: YC
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D001622:Betaine / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D050938:Glycine N-Methyltransferase / Q000302:isolation & purification / Q000378:metabolism*; D017019:Methanosarcinaceae / Q000201:enzymology*; D008969:Molecular Sequence Data; D013379:Substrate Specificity
chemical_list: D019843:Archaeal Proteins; D001622:Betaine; D050938:Glycine N-Methyltransferase