Molecular cloning of a thermo-alkaliphilic lipase from Bacillus subtilis DR8806: Expression and biochemical characterization

摘要

A thermo-alkaliphilic lipase from Bacillus subtilis DR8806 was functionally expressed as an N-terminal 6xHis-tagged recombinant enzyme in Escherichia coli BL21 using pET-28a(+) expression vector. Sequence analysis revealed an open reading frame of 639 bp encoding a 212-amino acid protein containing the well-conserved Ala-His-Ser-Met-Gly motif. One-step purification of the His-tagged recombinant lipase was achieved using Ni-NTA affinity chromatography with a specific activity of 1364U/mg. The purified enzyme with an apparent molecular mass of 26.8 kDa demonstrated the maximum activity at 70 ℃ and pH 8.0 for hydrolysis of p-nitrophenylbutyrate as substrate. The enzyme activity was strongly inhibited by divalent ions of heavy metals such as Hg~(2+) and Cu~(2+), while retained over 90% of the original activity in the presence of several reagents including DTNB (5,5'-dithiobis-(2-nitrobenzoic acid)), SDS (sodium dodecyl sulfate), urea, DMF (dimethylformamide), DTT (dithiothreitol), glycerol and Triton X-100. While being considerably stable in organic solvents, imidazolium-based ionic liquids (ILs) had stimulatory effects on the activity of purified lipase. Remarkable stabilization of enzyme at alkaline pH and in ionic liquids as well as its thermostability/thermoactivity are among the most fundamental characteristics which offer great potential for various biotechnological applications including detergent formulation, bioremediation processes and biotransformation in non-aqueous media.