Cloning, nucleotide sequencing and characterization of a polyurethanase gene (pueB) from Pseudomonas chlororaphis

A second gene (pueB, polyurethane esterase B) encoding an extracellular polyurethanase (PueB) was cloned from Pseudomonas chlororaphis into Escherichia coli. The recombinant polyurethanase showed esterase activity when assayed with various p-nitrophenyl substrates and lipase activity when assayed with triolein. Nucleotide sequencing of pueB showed an open reading frame of 1695 bp encoding a 60-kDa protein of 565 amino acid residues, with the serine hydrolase consensus sequence GXSXG and a C-terminal secretion signal (G-G-X-G-X-D-X-X-X). Unlike the PueA polyurethanase, PueB contains a putative N-terminal signal peptide. Comparison between the amino acid and nucleotide sequences of these two genes revealed that they share 42% and 59% identity respectfully. Parsimony analysis of the predicted amino acid sequences for the PueB, PueA, and other polyurethanase enzymes and similar lipase enzymes was performed. Interestingly the polyurethanase enzymes do not form a single cluster, but appear to be distributed among multiple lineages. These analyses suggest that the polyurethanase enzymes thus far studied have evolved from lipases, and are not derived from a single source.