Machida Shuntaro, Bakku Ranjith K, Suzuki Iwane
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
Front Microbiol. 2017 Oct 23;8:2061. doi: 10.3389/fmicb.2017.02061. eCollection 2017.
In living organisms, modified fatty acids are crucial for the functions of the cellular membranes and storage lipids where the fatty acids are esterified. Some bacteria produce a typical methyl-branched fatty acid, i.e., 10-methyl stearic acid (19:0Me10). The biosynthetic pathway of 19:0Me10 has not been demonstrated clearly yet. It had been speculated that 19:0Me10 is synthesized from oleic acid (18:1Δ9) by -adenosyl-L-methionine-dependent methyltransfer and NADPH-dependent reduction via a methylenated intermediate, 10-methyelene octadecanoic acid. Although the recombinant methyltransferases UmaA and UfaA1 from HRv synthesize 19:0Me10 from 18:1Δ9 and NADPH , these methyltransferases do not possess any domains functioning in the redox reaction. These findings may contradict the two-step biosynthetic pathway. We focused on novel -adenosyl-L-methionine-dependent methyltransferases from that are involved in 19:0Me10 synthesis and selected two candidate proteins, WP_048471942 and WP_048472121, by a comparative genomic analysis. However, the heterologous expression of these candidate genes in cells did not produce 19:0Me10. We found that one of the candidate genes, WP_048472121, was collocated with another gene, WP_048472120, that encodes a protein containing a domain associated with flavin adenine dinucleotide-binding oxidoreductase activity. The co-expression of these proteins (hereafter called BfaA and BfaB, respectively) led to the biosynthesis of 19:0Me10 in cells via the methylenated intermediate.
在生物体内，修饰脂肪酸对于细胞膜功能以及脂肪酸发生酯化反应的储存脂质至关重要。一些细菌会产生一种典型的甲基支链脂肪酸，即10 - 甲基硬脂酸（19:0Me10）。然而，19:0Me10的生物合成途径尚未得到明确证实。据推测，19:0Me10是由油酸（18:1Δ9）通过依赖于S - 腺苷 - L - 甲硫氨酸的甲基转移作用以及经由亚甲基化中间体10 - 亚甲基十八烷酸的依赖于NADPH的还原作用合成的。尽管来自幽门螺杆菌的重组甲基转移酶UmaA和UfaA1可从18:1Δ9和NADPH合成19:0Me10，但这些甲基转移酶并不具备在氧化还原反应中发挥作用的任何结构域。这些发现可能与两步生物合成途径相矛盾。我们聚焦于参与19:0Me10合成的来自幽门螺杆菌的新型依赖于S - 腺苷 - L - 甲硫氨酸的甲基转移酶，并通过比较基因组分析筛选出了两个候选蛋白，WP_048471942和WP_048472121。然而，这些候选基因在大肠杆菌细胞中的异源表达并未产生19:0Me10。我们发现其中一个候选基因WP_048472121与另一个基因WP_048472120相邻，后者编码一种含有与黄素腺嘌呤二核苷酸结合氧化还原酶活性相关结构域的蛋白。这些蛋白（以下分别称为BfaA和BfaB）的共表达导致大肠杆菌细胞中经由亚甲基化中间体合成了19:0Me10。
