Mechanism of <i>S</i>-Adenosyl-<scp>l</scp>-methionine <i>C</i>-Methylation by Cobalamin-dependent Radical <i>S</i>-Adenosyl-<scp>l</scp>-methionine Methylase in 1-Amino-2-methylcyclopropanecarboxylic Acid Biosynthesis
C-methylation of SAM in the biosynthesis of 1-amino-2-methylcyclopropanecarboxylic acid. Here, we determined that the methylation product is (4″R)-4″-methyl-SAM. Furthermore, we found that the 5′-deoxyadenosyl radical generated by Orf29 abstracts the pro-R hydrogen atom from the C-4″ position of SAM to generate the radical intermediate, which reacts with methylcobalamin to give (4″R)-4″-methyl-SAM
自由基S-腺苷-l-甲硫氨酸 (SAM) 甲基化酶 Orf29在 1-氨基-2-甲基环丙烷甲酸的生物合成中催化SAM 的C-甲基化。在这里,我们确定甲基化产物是(4″ R )-4″-甲基-SAM。此外,我们发现Orf29产生的5′-脱氧腺苷自由基从SAM的C-4”位上夺取pro-R氢原子,生成自由基中间体,该自由基中间体与甲钴胺反应生成(4” R )-4” -甲基-SAM。因此,证实Orf29催化的C-甲基化在构型保留的情况下进行。