Characterization of an Extracellular Lipase in Burkholderia sp. HY-10 Isolated from a Longicorn Beetle

Burkholderia sp. HY-10 isolated from the digestive tracts of the longicorn beetle, Prionus insularis, produced an extracellular lipase with a molecular weight of 33.5 kDa estimated by SDS-PAGE. The lipase was purified from the culture supernatant to near electrophoretic homogenity by a one-step adsorption-desorption procedure using a polypropylene matrix followed by a concentration step. The purified lipase exhibited highest activities at pH 8.5 and $60^{\circ}C$. A broad range of lipase substrates, from $C_4\;to\;C_{18}$ p-nitrophenyl esters, were hydrolyzed efficiently by the lipase. The most efficient substrate was p-nitrophenyl caproate ($C_6$). A 2485 bp DNA fragment was isolated by PCR amplification and chromosomal walking which encoded two polypeptides of 364 and 346 amino acids, identified as a lipase and a lipase foldase, respectively. The N-terminal amino acid sequence of the purified lipase and nucleotide sequence analysis predicted that the precursor lipase was proteolytically modified through the secretion step and produced a catalytically active 33.5 kDa protein. The deduced amino acid sequence for the lipase shared extensive similarity with those of the lipase family 1.2 of lipases from other bacteria. The deduced amino acid sequence contained two Cystein residues forming a disulfide bond in the molecule and three, well-conserved amino acid residues, $Ser^{131},\;His^{330},\;and\;Asp^{308}$, which composed the catalytic triad of the enzyme.