Abstract
Genome sequencing of cellulolytic myxobacterium Sorangium cellulosum reveals many open-reading frames (ORFs) encoding various degradation enzymes with low sequence similarity to those reported, but none of them has been characterized. In this paper, a predicted lipase gene (lipA) was cloned from S. cellulosum strain So0157-2 and characterized. lipA is 981-bp in size, encoding a polypeptide of 326 amino acids that contains the pentapeptide (GHSMG) and catalytic triad residues (Ser114, Asp250 and His284). Searching in the GenBank database shows that the LipA protein has only the 30% maximal identity to a human monoglyceride lipase. The novel lipA gene was expressed in Escherichia coli BL21 and the recombinant protein (r-LipA) was purified using Ni-NTA affinity chromatography. The enzyme hydrolyzed the p-nitrophenyl (pNP) esters of short or medium chain fatty acids (≤C10), and the maximal activity was on pNP acetate. The r- LipA is a cold-adapted lipase, with high enzymatic activity in a wide range of temperature and pH values. At 4 °C and 30 °C, the Km values of r-LipA on pNP acetate are 0.037 ± 0.001 and 0.174 ± 0.006 mM, respectively. Higher pH and temperature conditions promoted hydrolytic activity toward the pNP esters with longer chain fatty acids. Remarkably, this lipase retained much of its activity in the presence of commercial detergents and organic solvents. The results suggest that the r-LipA protein has some new characteristics potentially promising for industrial applications and S. cellulosum is an intriguing resource for lipase screening.
Highlights
Lipases/esterases are members of the α/β hydrolase superfamily, which is characterized by having a semi-conserved pentapeptide domain GXSXG (X represents any amino acid) and the Ser, Asp, His catalytic triad [1,2]
Characterization of the recombinant enzyme suggests that the purified r-LipA is a cold-adapted lipase which has some new characteristics potentially promising for industrial applications and the myxobacterial species S. cellulosum is an intriguing resource for lipase screening
We report the cloning of a novel lipase gene, lipA, from S. cellulosum So0157-2
Summary
Lipases/esterases are members of the α/β hydrolase superfamily, which is characterized by having a semi-conserved pentapeptide domain GXSXG (X represents any amino acid) and the Ser, Asp (or Glu), His catalytic triad [1,2]. In the majority of cold-adapted lipases, the optimum catalytic activity was around 20–40 °C and are stable at a wide range of temperatures. The cellulolytic myxobacterium Sorangium cellulosum is extremely interesting in drug screening, and almost half of the discovered myxobacterial secondary metabolites are produced by different strains of this species [17] In addition to these defined characteristics, S. cellulosum has excellent and extensive degradation ability on various macromolecules, including many different kinds of polysaccharide and lipid, of which the involved enzymes have been less investigated. The predicted products of these ORFs are all in low similarity to those studied lipases/esterases and none of them has been characterized, suggesting their potentially specific characteristics. Characterization of the recombinant enzyme suggests that the purified r-LipA is a cold-adapted lipase which has some new characteristics potentially promising for industrial applications and the myxobacterial species S. cellulosum is an intriguing resource for lipase screening
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