THE PSEUDOMONAS-FLUORESCENS LIPASE HAS A C-TERMINAL SECRETION SIGNAL AND IS SECRETED BY A 3-COMPONENT BACTERIAL ABC-EXPORTER SYSTEM

Both Pseudomonas aeruginosa and Pseudomonas fluorescens secrete a lipase into the extracellular medium. Unlike the lipase of P. aeruginosa, the lipase produced by P. fluorescens does not contain any N-terminal signal sequence. We show that the P. fluorescens lipase is secreted through the signal peptide-independent pathway of the alkaline protease that we previously identified in P. aeruginosa. Secretion of this protease (AprA) is dependent on the presence of three genes located adjacent to the aprA gene, aprD, aprE and aprF. The three secretion functions permit an efficient secretion of P. fluorescens lipase. Inactivation of one of them (AprE) prevented this secretion. In Escherichia coli, the three proteins AprD, AprE, AprF are necessary and sufficient for efficient secretion of lipase to the extracellular medium. The secretion signal is located within the C-terminal part of the lipase sequence and can promote efficient secretion of a passenger protein. Thus the P. fluorescens lipase secretion system belongs to the group of the three-component bacterial ABC-exporter systems.