Szilák L, Finta C, Patthy A, Venetianer P, Kiss A
Institute of Biochemistry, Hungarian Academy of Sciences, Szeged.
Nucleic Acids Res. 1994 Aug 11;22(15):2876-81. doi: 10.1093/nar/22.15.2876.
The DNA (cytosine-5)-methyltransferase (m5C-MTase) M.BspRI is able to accept the methyl group from the methyl donor S-adenosyl-L-methionine (AdoMet) in the absence of DNA. Transfer of the methyl group to the enzyme is a slow reaction relative to DNA methylation. Self-methylation is dependent on the native conformation of the enzyme and is inhibited by S-adenosyl-L-homocysteine, DNA and sulfhydryl reagents. Amino acid sequencing of proteolytic peptides obtained from M.BspRI, which had been methylated with [methyl-3H]AdoMet, and thin layer chromatography of the modified amino acid identified two cysteines, Cys156 and Cys181 that bind the methyl group in form of S-methylcysteine. One of the acceptor residues, Cys156 is the highly conserved cysteine which plays the role of the catalytic nucleophile of m5C-MTases.
DNA（胞嘧啶-5）-甲基转移酶（m5C-MTase）M.BspRI在不存在DNA的情况下能够从甲基供体S-腺苷-L-甲硫氨酸（AdoMet）接受甲基。相对于DNA甲基化，甲基向该酶的转移是一个缓慢的反应。自我甲基化取决于酶的天然构象，并受到S-腺苷-L-高半胱氨酸、DNA和巯基试剂的抑制。对用[甲基-3H]AdoMet甲基化的M.BspRI获得的蛋白水解肽进行氨基酸测序，以及对修饰氨基酸进行薄层色谱分析，确定了两个以S-甲基半胱氨酸形式结合甲基的半胱氨酸，即Cys156和Cys181。受体残基之一Cys156是高度保守的半胱氨酸，它在m5C-MTases中起催化亲核试剂的作用。
