Characterization of a novel lipase and its specific foldase from Acinetobacter sp. XMZ-26

A novel operon containing a lipase gene (lip26) and its specific foldase gene (lif26) was discovered from Acinetobacter sp. XMZ-26 by creating and screening a gene library and then using genome walking. The amino acid sequence of Lip26 and Lif26 showed only 46.4% and 37.3% identity with the LipA and LipB (Lif) sequences from Acinetobacter sp. SY-01, respectively. The expressed recombinant Lip26 formed inactive inclusion bodies in Escherichia coli. However, the active Lip26 was refolded by the dilution refolding method with the assistance of purified recombinant Lif26, and the refolded Lip26 had a high specific activity. Lip26 hydrolyzed p-nitrophenyl (pNP) esters of fatty acids with C₂ to C₁₆ acyl chain lengths and had a substrate preference for pNP myristate. Maximal Lip26 activity was dependent on both the temperature (55 °C) and pH (9.0). In addition, Lip26 was capable of maintaining its activity in the presence of many detergents and organic solutions, and its activity was enhanced by the presence of Ca²⁺, Mn²⁺, and Ba²⁺. To directly obtain active Lip26, an E. coli strain was co-transformed with two expression plasmids containing the lip26 and lif26 genes. The co-expression of both proteins in vivo resulted in the expression of half of the recombinant Lip26 as a soluble protein with demonstrable lipase activity. A direct protein interaction between Lif26 and Lip26A was detected by both a pull-down assay and a yeast two-hybrid experiment.