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Biochemical and molecular characterization of the Pseudomonas lemoignei polyhydroxyalkanoate depolymerase system
D Jendrossek1, A Frisse, A Behrends
1Institut für Mikrobiologie, Georg-August-Universität zu Göttingen, Germany.
Journal of Bacteriology
|February 1, 1995
Summary
Pseudomonas lemoignei possesses five polyhydroxyalkanoate (PHA) depolymerase genes. Researchers identified and characterized these genes, revealing conserved catalytic domains and distinct substrate specificities for PHB and PHV hydrolysis.
Area of Science:
- Microbiology and Molecular Biology
- Biochemistry and Enzymology
- Polymer Science
Background:
- Pseudomonas lemoignei produces five distinct polyhydroxyalkanoate (PHA) depolymerase genes (phaZ1-phaZ5).
- These genes encode extracellular enzymes responsible for degrading poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyvalerate) (PHV).
Purpose of the Study:
- To identify and characterize the fifth PHA depolymerase gene (phaZ5) in P. lemoignei.
- To determine the nucleotide sequences and analyze the deduced amino acid sequences of phaZ5 and phaZ4.
- To investigate the structural and functional relationships among P. lemoignei PHA depolymerases and those from other bacterial species.
Main Methods:
- Gene identification using colony hybridization with a phaZ5-specific oligonucleotide.
- Nucleotide sequencing of cloned DNA fragments (EcoRI for phaZ5, BamHI for phaZ4).
- Bioinformatic analysis of open reading frames (ORFs) and deduced amino acid sequences.
- Subcloning and expression of phaZ1 in other bacterial strains (A. eutrophus).
- Purification and characterization of recombinant and wild-type PHA depolymerases.
Main Results:
- The phaZ5 gene encodes the precursor of PHB depolymerase A, and phaZ4 encodes a PHV depolymerase precursor.
- Analysis revealed conserved domain structures, including signal peptides, catalytic domains with putative catalytic triads, and variable C-terminal regions.
- PHA depolymerases exhibited substrate specificities for PHB, PHV, and poly(4-hydroxybutyrate), with varying efficiencies.
- Wild-type depolymerases were glycosylated, while recombinant versions were not; PHB hydrolysis required divalent cations like Ca2+.
Conclusions:
- The study elucidated the genetic and structural basis of PHA depolymerases in P. lemoignei.
- Conserved structural motifs suggest a common evolutionary origin and catalytic mechanism for these enzymes.
- Distinct C-terminal regions likely determine substrate specificity, differentiating PHB and PHV hydrolysis.