Hyakutake Manami, Tomizawa Satoshi, Mizuno Kouhei, Abe Hideki, Tsuge Takeharu
Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Japan.
Appl Environ Microbiol. 2014 Feb;80(4):1421-9. doi: 10.1128/AEM.03576-13. Epub 2013 Dec 13.
Polyhydroxyalkanoate (PHA)-producing Bacillus strains express class IV PHA synthase, which is composed of the subunits PhaR and PhaC. Recombinant Escherichia coli expressing PHA synthase from Bacillus cereus strain YB-4 (PhaRCYB-4) showed an unusual reduction of the molecular weight of PHA produced during the stationary phase of growth. Nuclear magnetic resonance analysis of the low-molecular-weight PHA revealed that its carboxy end structure was capped by ethanol, suggesting that the molecular weight reduction was the result of alcoholytic cleavage of PHA chains by PhaRCYB-4 induced by endogenous ethanol. This scission reaction was also induced by exogenous ethanol in both in vivo and in vitro assays. In addition, PhaRCYB-4 was observed to have alcoholysis activity for PHA chains synthesized by other synthases. The PHA synthase from Bacillus megaterium (PhaRCBm) from another subgroup of class IV synthases was also assayed and was shown to have weak alcoholysis activity for PHA chains. These results suggest that class IV synthases may commonly share alcoholysis activity as an inherent feature.
产聚羟基脂肪酸酯（PHA）的芽孢杆菌菌株表达IV类PHA合酶，其由亚基PhaR和PhaC组成。表达来自蜡样芽孢杆菌菌株YB-4的PHA合酶（PhaRCYB-4）的重组大肠杆菌在生长稳定期产生的PHA分子量出现异常降低。对低分子量PHA的核磁共振分析表明，其羧基末端结构被乙醇封端，这表明分子量降低是内源性乙醇诱导PhaRCYB-4对PHA链进行醇解裂解的结果。在体内和体外试验中，外源性乙醇也诱导了这种裂解反应。此外，观察到PhaRCYB-4对其他合酶合成的PHA链具有醇解活性。还对来自IV类合酶另一个亚组的巨大芽孢杆菌的PHA合酶（PhaRCBm）进行了测定，结果表明其对PHA链具有较弱的醇解活性。这些结果表明，IV类合酶可能普遍具有醇解活性这一固有特征。
