Evidence that a linear megaplasmid encodes enzymes of aliphatic alkene and epoxide metabolism and coenzyme M (2-mercaptoethanesulfonate) biosynthesis in Xanthobacter strain Py2
Evidence that a linear megaplasmid encodes enzymes of aliphatic alkene and epoxide metabolism and coenzyme M (2-mercaptoethanesulfonate) biosynthesis in Xanthobacter strain Py2
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DOI：
10.1128/jb.183.7.2172-2177.2001
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发表时间：
2001-04-01
影响因子：
3.2
通讯作者：
Ensign, SA
中科院分区：
文献类型：
--
作者：
Krum, JG;Ensign, SA
丙烯的细菌代谢是通过环氧化反应生成环氧丙烷，接着是一系列的三个反应，导致环氧化物开环和羧基化形成乙酰乙酸。辅酶M（2-巯基乙烷磺酸）（CoM）在环氧化物羧化过程中起核心作用，作为环氧化物开环的亲核试剂和C-3单元的载体，最终羧化成乙酰乙酸，释放CoM。在本研究中，在革兰氏阴性细菌Xanthobacter菌株Py2中鉴定了一个320 kb的线性巨型质粒，该质粒含有编码丙烯氧化和环氧化物羧化关键酶的基因。在非选择性条件下，即以葡萄糖或醋酸盐作为碳源，在不含丙烯的情况下，反复培养黄杆菌菌株Py2，导致丙烯阳性表型的丧失。丙烯负表型与320 kb线性巨质粒丧失、烯烃单加氧酶和环氧化物羧化酶的诱导和表达活性丧失以及CoM生物合成能力丧失相关。对四种环氧化羧化酶基因下游基因编码的假设蛋白（XecG）进行序列分析，发现其序列与产甲烷古细菌热自养甲烷细菌、jannaschii甲烷球菌和枯草芽孢杆菌中尚未指定功能的蛋白高度一致。M. Graupner， H. Xu， R. H. White， J.中华微生物学杂志，2002,18 (2):462 - 467,2000). jannaschii的XecG同源基因MJ0255位于一个编码CoM生物合成关键酶的基因MJ0256附近。我们提出，黄杆菌菌株Py2的丙烯阳性表型依赖于含有烯烃氧化、环氧化物羧化和CoM生物合成关键酶基因的线性大质粒的选择性维持。
The bacterial metabolism of propylene proceeds by epoxidation to epoxypropane followed by a sequence of three reactions resulting in epoxide ring opening and carboxylation to form acetoacetate. Coenzyme M (2-mercaptoethanesulfonic acid) (CoM) plays a central role in epoxide carboxylation by serving as the nucleophile for epoxide ring opening and the carrier of the C-3 unit that is ultimately carboxylated to acetoacetate, releasing CoM. In the present work, a 320-kb linear megaplasmid has been identified in the gram negative bacterium Xanthobacter strain Py2, which contains the genes encoding the key enzymes of propylene oxidation and epoxide carboxylation. Repeated subculturing of Xanthobacter strain Py2 under nonselective conditions, i.e., with glucose or acetate as the carbon source in the absence of propylene, resulted in the loss of the propylene-positive phenotype. The propylene-negative phenotype correlated with the loss of the 320-kb linear megaplasmid, loss of induction and expression of alkene monooxgenase and epoxide carboxylation enzyme activities, and the loss of CoM biosynthetic capability. Sequence analysis of a hypothetical protein (XecG), encoded by a gene located downstream of the genes for the four enzymes of epoxide carboxylation, revealed a high degree of sequence identity with proteins of as-yet unassigned functions in the methanogenic archaea Methanobacterium thermoautotrophicum and Methanococcus jannaschii and in Bacillus subtilis. The M. jannaschii homolog of XecG, MJ0255, is located next to a gene, MJ0256, that has been shown to encode a key enzyme of CoM biosynthesis (M. Graupner, H. Xu, and R. H. White, J. Bacteriol. 182: 4862-4867, 2000). We propose that the propylene-positive phenotype of Xanthobacter strain Py2 is dependent on the selective maintenance of a linear megaplasmid containing the genes for the key enzymes of alkene oxidation, epoxide carboxylation, and CoM biosynthesis.