Background
Microorganisms are the most proficient decomposers in nature, using secreted enzymes in the hydrolysis of lignocellulose. As such, they present the most abundant source for discovery of new enzymes. Acremonium alcalophilum is the only known cellulolytic fungus that thrives in alkaline conditions and can be cultured readily in the laboratory. Its optimal conditions for growth are 30°C and pH 9.0-9.2. The genome sequence of Acremonium alcalophilum has revealed a large number of genes encoding biomass-degrading enzymes. Among these enzymes, lipases are interesting because of several industrial applications including biofuels, detergent, food processing and textile industries.
Conclusion
Besides being the first heterologous expression and characterization of a gene coding for a lipase from A. alcalophilum, this report shows that LipA is very versatile exhibiting both acetylxylan esterase and lipase activities potentially useful for diverse industry sectors, and that tobacco is a suitable bioreactor for producing fungal proteins.
Results
We identified a lipA gene in the genome sequence of Acremonium alcalophilum, encoding a protein with a predicted lipase domain with weak sequence identity to characterized enzymes. Unusually, the predicted lipase displays ≈ 30% amino acid sequence identity to both feruloyl esterase and lipase of Aspergillus niger. LipA, when transiently produced in Nicotiana benthamiana, accumulated to over 9% of total soluble protein. Plant-produced recombinant LipA is active towards p-nitrophenol esters of various carbon chain lengths with peak activity on medium-chain fatty acid (C8). The enzyme is also highly active on xylose tetra-acetate and oat spelt xylan. These results suggests that LipA is a novel lipolytic enzyme that possesses both lipase and acetylxylan esterase activity. We determined that LipA is a glycoprotein with pH and temperature optima at 8.0 and 40°C, respectively.