Aguilar J A, Zavala A N, Díaz-Pérez C, Cervantes C, Díaz-Pérez A L, Campos-García J
Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Edif. B-3, Ciudad Universitaria, CP 58030, Morelia, Michoacán, Mexico.
Appl Environ Microbiol. 2006 Mar;72(3):2070-9. doi: 10.1128/AEM.72.3.2070-2079.2006.
Evidence suggests that the Pseudomonas aeruginosa PAO1 gnyRDBHAL cluster, which is involved in acyclic isoprenoid degradation (A. L. Díaz-Pérez, N. A. Zavala-Hernández, C. Cervantes, and J. Campos-García, Appl. Environ. Microbiol. 70:5102-5110, 2004), corresponds to the liuRABCDE cluster (B. Hoschle, V. Gnau, and D. Jendrossek, Microbiology 151:3649-3656, 2005). A liu (leucine and isovalerate utilization) homolog cluster was found in the PAO1 genome and is related to the catabolism of acyclic monoterpenes of the citronellol family (AMTC); it was named the atu cluster (acyclic terpene utilization), consisting of the atuCDEF genes and lacking the hydroxymethyl-glutaryl-coenzyme A (CoA) lyase (HMG-CoA lyase) homolog. Mutagenesis of the atu and liu clusters showed that both are involved in AMTC and leucine catabolism by encoding the enzymes related to the geranyl-CoA and the 3-methylcrotonyl-CoA pathways, respectively. Intermediary metabolites of the acyclic monoterpene pathway, citronellic and geranic acids, were accumulated, and leucine degradation rates were affected in both atuF and liuD mutants. The alpha subunit of geranyl-CoA carboxylase and the alpha subunit of 3-methylcrotonyl-CoA carboxylase (alpha-MCCase), encoded by the atuF and liuD genes, respectively, were both induced by citronellol, whereas only the alpha-MCCase subunit was induced by leucine. Both citronellol and leucine also induced a LacZ transcriptional fusion at the liuB gene. The liuE gene encodes a probable hydroxy-acyl-CoA lyase (probably HMG-CoA lyase), an enzyme with bifunctional activity that is essential for both AMTC and leucine degradation. P. aeruginosa PAO1 products encoded by the liuABCD cluster showed a higher sequence similarity (77.2 to 79.5%) with the probable products of liu clusters from several Pseudomonas species than with the atuCDEF cluster from PAO1 (41.5%). Phylogenetic studies suggest that the atu cluster from P. aeruginosa could be the result of horizontal transfer from Alphaproteobacteria. Our results suggest that the atu and liu clusters are bifunctional operons involved in both the AMTC and leucine catabolic pathways.
有证据表明，铜绿假单胞菌PAO1的gnyRDBHAL基因簇参与无环类异戊二烯的降解（A. L. Díaz-Pérez、N. A. Zavala-Hernández、C. Cervantes和J. Campos-García，《应用与环境微生物学》，2004年，第70卷，第5102 - 5110页），它与liuRABCDE基因簇相对应（B. Hoschle、V. Gnau和D. Jendrossek，《微生物学》，2005年，第151卷，第3649 - 3656页）。在PAO1基因组中发现了一个liu（亮氨酸和异戊酸利用）同源基因簇，它与香茅醇家族的无环单萜类化合物（AMTC）的分解代谢有关；它被命名为atu基因簇（无环萜烯利用），由atuCDEF基因组成，并且缺少羟甲基 - 戊二酰辅酶A（CoA）裂解酶（HMG - CoA裂解酶）的同源物。atu和liu基因簇的诱变表明，它们都通过分别编码与香叶基 - CoA和3 - 甲基巴豆酰 - CoA途径相关的酶而参与AMTC和亮氨酸的分解代谢。无环单萜途径的中间代谢产物香茅酸和香叶酸积累，并且atuF和liuD突变体中的亮氨酸降解速率都受到影响。分别由atuF和liuD基因编码的香叶基 - CoA羧化酶的α亚基和3 - 甲基巴豆酰 - CoA羧化酶（α - MCCase）的α亚基都由香茅醇诱导，而只有α - MCCase亚基由亮氨酸诱导。香茅醇和亮氨酸还都诱导了liuB基因处的LacZ转录融合。liuE基因编码一种可能的羟酰基 - CoA裂解酶（可能是HMG - CoA裂解酶），这是一种对AMTC和亮氨酸降解都至关重要的具有双功能活性的酶。由liuABCD基因簇编码产生的铜绿假单胞菌PAO1产物与几种假单胞菌属物种的liu基因簇的可能产物的序列相似性更高（77.2%至79.5%），而与PAO1的atuCDEF基因簇的相似性为41.5%。系统发育研究表明，铜绿假单胞菌的atu基因簇可能是从α - 变形菌门水平转移的结果。我们的结果表明，atu和liu基因簇是参与AMTC和亮氨酸分解代谢途径的双功能操纵子。
