Cloning and characterization of the poly(hydroxyalkanoic acid)‐depolymerase gene locus, phaZ1, of Pseudomonas lemoignei and its gene product

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Abstract
Four different DNA fragments each coding for poly(hydroxyalkanoic acid) depolymerase (phaZ1–phaZ4) were isolated in pUC plasmids from a genomic library of Pseudomonas lemoignei in Escherichia coli. All recombinant strains secreted a highly active poly(3-hydroxybutyric acid) depolymerase and produced large translucent halos on an opaque medium containing poly(3-hydroxybutyric acid) granules. One DNA region (phaZ1) was present in seven independently isolated clones. Three other cloned DNA fragments were different from phaZ1 and from each other (phaZ2–phaZ4). In phaZ1, an open-reading frame of 1245 bp was identified from the nucleotide sequence of a 5435-bp MboI fragment (57 mol G+C/100 mol) of this region and encoded a novel poly(hydroxyalkanoic acid) depolymerase of P. lemoignei, poly(3-hydroxybutyric acid) depolymerase C. A leader-sequence peptidase-cleavage site was predicted from the deduced amino acid sequence between Ala37 and Leu38. The calculated relative molecular masses of the precursor and the putative mature protein were 43468 and 39581, respectively. The polypeptide contains a lipase consensus sequence (Gly-Xaa-Ser-Xaa-Gly) and an unusually high proportion of threonine residues (22 of 36 amino acids) near the C-terminus. The N-terminus of the deduced amino acid sequence of PhaZ1 differed from that of the purified poly(3-hydroxybutyric acid) depolymerases A, B and the poly(3-hydroxyvaleric acid) depolymerase of P. lemoignei. The phaZ1 gene product, poly(3-hydroxybutyric acid) depolymerase C, was partially purified from recombinant E. coli (pUC91 ::phaZ1). The purified protein was specific for poly(hydroxyalkanoic acid) consisting of monomers of four or five carbon atoms and for p-nithrophenylbutyrate as substrates. The polymer-hydrolyzing activity, but not the p-nitrophenylate esterase activity, was inhibited by complex media such as Luria-Bertani medium and by soluble E. coli proteins. The enzyme protein did not cross-react with antibodies raised against purified poly(3-hydroxyvaleric acid) depolymerase of P. lemoignei.