Takaku Hiroaki, Kimoto Ayumi, Kodaira Shoko, Nashimoto Masayuki, Takagi Masamichi
Department of Applied Life Sciences, Niigata University of Pharmacy and Applied Life Sciences, Niigata, Japan.
FEMS Microbiol Lett. 2006 Nov;264(2):152-9. doi: 10.1111/j.1574-6968.2006.00448.x.
A Gram-positive poly(3-hydroxybutyrate) (PHB)-degrading bacterial strain was isolated from compost. This organism, identified as Bacillus megaterium N-18-25-9, produced a clearing zone on opaque NB-PHB agar, indicating the presence of extracellular PHB depolymerase. A PHB depolymerase gene, PhaZ(Bm), of B. megaterium N-18-25-9 was cloned and sequenced, and the recombinant gene product was purified from Escherichia coli. The N-terminal half region of PhaZ(Bm) shared significant homologies with a catalytic domain of other PHB depolymerases. Although the C-terminal half region of PhaZ(Bm) showed no significant similarity with those of other PHB depolymerases, that region was necessary for the PHB depolymerase activity. Therefore, this enzyme's domain structure is unique among extracellular PHB depolymerase domain structures. The addition of PHB to the medium led to a sixfold increase in PhaZ(Bm) mRNA, while the presence of glucose repressed PhaZ(Bm) expression. The maximum activity was observed at pH 9.0 at 65 degrees C.
从堆肥中分离出一株革兰氏阳性聚（3-羟基丁酸酯）（PHB）降解细菌菌株。该菌株被鉴定为巨大芽孢杆菌N-18-25-9，在不透明的NB-PHB琼脂上产生了一个透明圈，表明存在细胞外PHB解聚酶。克隆并测序了巨大芽孢杆菌N-18-25-9的PHB解聚酶基因PhaZ(Bm)，并从大肠杆菌中纯化了重组基因产物。PhaZ(Bm)的N端半区与其他PHB解聚酶的催化结构域具有显著同源性。虽然PhaZ(Bm)的C端半区与其他PHB解聚酶的C端半区没有显著相似性，但该区域对于PHB解聚酶活性是必需的。因此，这种酶的结构域结构在细胞外PHB解聚酶结构域结构中是独特的。向培养基中添加PHB导致PhaZ(Bm) mRNA增加了六倍，而葡萄糖的存在则抑制了PhaZ(Bm)的表达。在65℃、pH 9.0时观察到最大活性。
