Biochemical evidence that phaZ gene encodes a specific intracellular medium chain length polyhydroxyalkanoate depolymerase in Pseudomonas putida KT2442 -: Characterization of a paradigmatic enzyme

被引:70
作者
de Eugenio, Laura I.
Garcia, Pedro
Luengo, Jose M.
Sanz, Jesus M.
San Roman, Julio
Garcia, Jose Luis
Prieto, Maria A.
机构
[1] CSIC, Ctr Invest Biol, Dept Mol Microbiol, E-28040 Madrid, Spain
[2] Univ Leon, Dept Bioquim & Biol Mol, E-24007 Leon, Spain
[3] Univ Miguel Hernandez, Inst Biol Mol & Celular, Alicante 03202, Spain
[4] CSIC, Inst Ciencia & Tecnol Polimeros, E-28006 Madrid, Spain
关键词
D O I
10.1074/jbc.M608119200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Polyhydroxyalkanoates (PHAs) can be catabolized by many microorganisms using intra- or extracellular PHA depolymerases. Most of our current knowledge of these intracellular enzyme-coding genes comes from the analysis of short chain length PHA depolymerases, whereas medium chain length PHA (mcl-PHA) intracellular depolymerization systems still remained to be characterized. The phaZ gene of some Pseudomonas putida strains has been identified only by mutagenesis and complementation techniques as putative intracellular mcl-PHA depolymerase. However, none of their corresponding encoded PhaZ enzymes have been characterized in depth. In this study the PhaZ depolymerase from P. putida KT2442 has been purified and biochemically characterized after its overexpression in Escherichia coli. To facilitate these studies we have developed a new and very sensitive radioactive method for detecting PHA hydrolysis in vitro. We have demonstrated that PhaZ is an intracellular depolymerase that is located in PHA granules and that hydrolyzes specifically mcl-PHAs containing aliphatic and aromatic monomers. The enzyme behaves as a serine hydrolase that is inhibited by phenylmethylsulfonyl fluoride. We have modeled the three-dimensional structure of PhaZ complexed with a 3-hydroxyoctanoate dimer. Using this model, we found that the enzyme appears to be built up from a core alpha/beta hydrolase-type domain capped with a lid structure with an active site containing a catalytic triad buried near the connection between domains. All these data constitute the first biochemical characterization of PhaZ and allow us to propose this enzyme as the paradigmatic representative of intracellular endo/exo-mcl-PHA depolymerases.
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页码:4951 / 4962
页数:12
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