ABC transporter for lipase and protease in pseudomonas fluorescens

Abstract

Pseudomonas fluorescens, a gram negative psychrotrophic bacterium, secretes a thermostable lipase into the extracellular medium. In our previous study, the lipase of P. fluorescens SIK W1 was cloned and expressed in Escherichia coli, but it accumulated as inactive inclusion bodies. Amino acid sequence analysis of the lipase revealed a potential C-terminal targeting sequence recognized by ABC transporter. Genetic loci around the lipase gene were searched and a secretory gene was identified. Nucleotide sequencing of a 8.5-kb DNA fragment revealed three components of the ABC transporter, tliD, tliE and tliF upstream of the lipase gene, tliA. In addition, genes encoding a protease and a protease inhibitor were located upstream of tliDEF. A transcriptional terminator downstream of prtA and a putative promoter upstream of tliDEF revealed that tliA and tliDEF are organized as an operon. The TliDEF showed high similarity with ABC transporters of Pseudomonas aeruginosa alkaline protease, Erwinia chrysanthemi protease, Serratia marcescens lipase and Pseudomonas fluorescens CY091 protease. The tliDEF and the lipase structural gene in a single operon were sufficient for E. coli cells to secrete the lipase. In addition, E. coli harboring the lipase gene secreted the lipase by complementation of tliDEF in a different plasmid. The protease was also secreted by complementation of tliDEF in E. coli. The ABC transporter of P. fluorescens was optimally functional at 20℃ and 25℃ while the ABC transporter, aprD, aprE and aprF, of P. aeruginosa secreted the lipase and the protease irrespective of temperature between 20 to 37℃. These results demonstrated that the lipase and the protease are secreted by the ABC transporter in P. fluorescens SIK W1 and its secretory function is temperature dependent.