C-Methylation of S-adenosyl-L-Methionine Occurs Prior to Cyclopropanation in the Biosynthesis of 1-Amino-2-Methylcyclopropanecarboxylic Acid (Norcoronamic Acid) in a Bacterium
C-Methylation of S-adenosyl-L-Methionine Occurs Prior to Cyclopropanation in the Biosynthesis of 1-Amino-2-Methylcyclopropanecarboxylic Acid (Norcoronamic Acid) in a Bacterium
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DOI：
10.3390/biom10050775
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发表时间：
2020-05-01
期刊：
影响因子：
5.5
通讯作者：
Hamano, Yoshimitsu
中科院分区：
文献类型：
--
作者：
Maruyama, Chitose;Chinone, Yukiko;Hamano, Yoshimitsu
许多重要的肽来源于细菌或真菌，含有非蛋白质氨基酸（NPA）结构单元。最近，据报道，在细菌中，含环丙烷的NPA 1-氨基环丙烷羧酸（ACC）是由S-腺苷-L-甲硫氨酸（SAM）的L-甲硫氨酸部分通过非经典ACC形成酶产生的。另一方面，已经提出单甲基化ACC类似物2-甲基-ACC（MeACC）衍生自L-缬氨酸。因此，我们通过鉴定含有细菌MeACC合酶基因的基因簇来研究MeACC的生物合成。在这个基因簇中，我们确定了两个基因，orf 29和orf 30，分别编码钴胺素（B12）依赖的自由基SAM甲基转移酶和细菌ACC合酶，并被发现参与MeACC的生物合成。使用其重组酶（rOrf 29和rOrf 30）的体外分析进一步揭示MeACC的ACC结构源自SAM的L-甲硫氨酸部分，而不是L-缬氨酸。此外，发现rOrf 29催化SAM的L-甲硫氨酸部分的C-甲基化。然后通过rOrf 30将所得SAM的甲基化衍生物转化为MeACC。因此，我们证明，SAM的C-甲基化发生在环丙烷化之前，在细菌MeACC（norcoronamic acid）的生物合成中。
Many pharmacologically important peptides are bacterial or fungal in origin and contain nonproteinogenic amino acid (NPA) building blocks. Recently, it was reported that, in bacteria, a cyclopropane-containing NPA 1-aminocyclopropanecarboxylic acid (ACC) is produced from the L-methionine moiety of S-adenosyl-L-methionine (SAM) by non-canonical ACC-forming enzymes. On the other hand, it has been suggested that a monomethylated ACC analogue, 2-methyl-ACC (MeACC), is derived from L-valine. Therefore, we have investigated the MeACC biosynthesis by identifying a gene cluster containing bacterial MeACC synthase genes. In this gene cluster, we identified two genes, orf29 and orf30, which encode a cobalamin (B12)-dependent radical SAM methyltransferase and a bacterial ACC synthase, respectively, and were found to be involved in the MeACC biosynthesis. In vitro analysis using their recombinant enzymes (rOrf29 and rOrf30) further revealed that the ACC structure of MeACC was derived from the L-methionine moiety of SAM, rather than L-valine. In addition, rOrf29 was found to catalyze the C-methylation of the L-methionine moiety of SAM. The resulting methylated derivative of SAM was then converted into MeACC by rOrf30. Thus, we demonstrate that C-methylation of SAM occurs prior to cyclopropanation in the biosynthesis of a bacterial MeACC (norcoronamic acid).