Multiple beta-ketothiolases mediate poly(beta-hydroxyalkanoate) copolymer synthesis in Ralstonia eutropha.
Multiple beta-ketothiolases mediate poly(beta-hydroxyalkanoate) copolymer synthesis in Ralstonia eutropha.
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发表时间：
1998
影响因子：
3.2
通讯作者：
S. Slater;K. Houmiel;M. Tran;T. Mitsky;N. Taylor;S. Padgette;K. Gruys
中科院分区：
文献类型：
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作者：
S. Slater;K. Houmiel;M. Tran;T. Mitsky;N. Taylor;S. Padgette;K. Gruys
聚羟基烷酸酯(PHAs)是一类碳储能聚合物，由多种细菌在环境限制下产生。产生的聚合物的类型取决于可用碳源、有机体中间代谢的灵活性以及PHA生物合成酶的底物专一性。富营养拉尔斯氏菌既能产生均聚物聚-β-羟基丁酸酯，又能在提供适当底物的情况下产生共聚物poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate)。生产PHBV羟基戊酸酯部分的一个必要步骤是乙酰辅酶A(乙酰辅酶A)和丙酰辅酶A缩合形成β-酮戊酰辅酶A。这种活性通常被归因于由真核细菌phbA编码的β-酮硫解酶。然而，我们已经确定PhbA对催化这种缩合反应没有显著贡献。在这里，我们报道了bktB基因的克隆和遗传分析，该基因编码富营养化红假单胞菌的β-酮硫醇酶，能够形成β-酮戊酰辅酶A。遗传分析确定BktB是主要的缩合酶，导致丙酰辅酶A衍生的β-羟基戊酸酯的产生。我们还报告了一种额外的β-酮硫醇酶，命名为BktC，可能是产生β-羟基戊酸酯的第二条途径。
Polyhydroxyalkanoates (PHAs) are a class of carbon and energy storage polymers produced by numerous bacteria in response to environmental limitation. The type of polymer produced depends on the carbon sources available, the flexibility of the organism's intermediary metabolism, and the substrate specificity of the PHA biosynthetic enzymes. Ralstonia eutropha produces both the homopolymer poly-beta-hydroxybutyrate (PHB) and, when provided with the appropriate substrate, the copolymer poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV). A required step in production of the hydroxyvalerate moiety of PHBV is the condensation of acetyl coenzyme A (acetyl-CoA) and propionyl-CoA to form beta-ketovaleryl-CoA. This activity has generally been attributed to the beta-ketothiolase encoded by R. eutropha phbA. However, we have determined that PhbA does not significantly contribute to catalyzing this condensation reaction. Here we report the cloning and genetic analysis of bktB, which encodes a beta-ketothiolase from R. eutropha that is capable of forming beta-ketovaleryl-CoA. Genetic analyses determined that BktB is the primary condensation enzyme leading to production of beta-hydroxyvalerate derived from propionyl-CoA. We also report an additional beta-ketothiolase, designated BktC, that probably serves as a secondary route toward beta-hydroxyvalerate production.