Overproduction in Escherichia coli, purification and characterization of a family I.3 lipase from Pseudomonas sp MIS38

Determination of the nucleotide sequence of the gene encoding a lipase from Pseudomonas sp. MIS38 (PML) revealed that PML is a member of the lipase family I.3 and is composed of 617 amino acid residues with a calculated molecular weight of 64 510. Recombinant PML (rPML) was overproduced in Escherichia coli in an insoluble form, solubilized in the presence of 8 M urea, purified in a urea-denatured form and refolded by removing urea in the presence of the Ca2+ ion. Gel filtration chromatography suggests that this refolded protein is monomeric. rPML showed relatively broad substrate specificities and hydrolyzed glyceryl tributyrate and olive oil with comparable efficiencies. rPML was active only in the form of a holoenzyme, in which at least 12 Ca2+ ions bound. These Ca2+ ions bound too tightly to be removed from the protein upon dialysis, but were removed from it upon EDTA treatment. The resultant ape-enzyme was fully active in the presence of 10 mM CaCl2, but was inactive in the absence of the Ca2+ ion. PML has a GXSXG motif, which is conserved in lipases/esterases and generally contains the active-site serine. The mutation of Ser(207) within this motif to Ala completely inactivated PML, suggesting that Ser(207) is the active-site serine of PML. (C) 2000 Elsevier Science B.V. All rights reserved.