Formaldehyde-detoxifying role of the tetrahydromethanopterin-linked pathway in Methylobacterium extorquens AM1
Formaldehyde-detoxifying role of the tetrahydromethanopterin-linked pathway in Methylobacterium extorquens AM1
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DOI：
10.1128/jb.185.23.7160-7168.2003
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发表时间：
2003-12-01
影响因子：
3.2
通讯作者：
Lidstrom, ME
中科院分区：
文献类型：
--
作者：
Marx, CJ;Chistoserdova, L;Lidstrom, ME
在甲醛和甲酸盐之间的C-1转移中，兼性甲基杆菌AM1具有两条依赖蝶呤的途径，即四氢叶酸(H4F)连接途径和四氢甲烷蝶呤(H4MPT)连接途径。这两条途径都是在C-1底物上生长所必需的；然而，H4MPT途径缺陷的突变株显示出一种独特的表型，即在多碳化合物(如琥珀酸)上生长时受到甲醇的抑制。此前有人提出，这种对甲醇敏感的表型是由于无法有效解毒甲醇产生的甲醛所致。在这里，我们提出了四个H4MPT途径缺陷突变的比较生理学特征，并将它们归入三个不同的表型类别，这三个表型类别与各自酶的生化作用相一致。我们的研究表明，Extorquens AM1中存在的类似的H4F途径不能完成甲醛解毒功能，而与谷胱甘肽和NAD(+)连锁的异源表达途径可以成功地替代H4MPT途径。此外，在以前被认为是必需的基因中产生了零突变，这表明在多碳化合物的生长过程中并不是绝对需要H4MPT途径。这些结果明确了H4MPT途径在Extorquens AM1中作为主要的甲醛氧化和解毒途径的作用。
The facultative methylotroph Methylobacterium extorquens AM1 possesses two pterin-dependent pathways for C-1 transfer between formaldehyde and formate, the tetrahydrofolate (H4F)-linked pathway and the tetrahydromethanopterin (H4MPT)-linked pathway. Both pathways are required for growth on C-1 substrates; however, mutants defective for the H4MPT pathway reveal a unique phenotype of being inhibited by methanol during growth on multicarbon compounds such as succinate. It has been previously proposed that this methanol-sensitive phenotype is due to the inability to effectively detoxify formaldehyde produced from methanol. Here we present a comparative physiological characterization of four mutants defective in the H4MPT pathway and place them into three different phenotypic classes that are concordant with the biochemical roles of the respective enzymes. We demonstrate that the analogous H4F pathway present in M. extorquens AM1 cannot fulfill the formaldehyde detoxification function, while a heterologously expressed pathway linked to glutathione and NAD(+) can successfully substitute for the H4MPT pathway. Additionally, null mutants were generated in genes previously thought to be essential, indicating that the H4MPT pathway is not absolutely required during growth on multicarbon compounds. These results define the role of the H4MPT pathway as the primary formaldehyde oxidation and detoxification pathway in M. extorquens AM1.