Bacterial lipases from Pseudomonas: Regulation of gene expression and mechanisms of secretion

Lipases from Pseudomonas bacteria are widely used for a variety of biotechn ological applications. Overexpression in heterologous hosts Like Escherichi a coli failed to produce enzymatically active lipase prompting to study the molecular mechanisms underlying the regulation of lipase gene expression a nd secretion. The prototype lipase from P. aeruginosa is encoded in a bicis tronic operon which is transcribed from two different promoters, one of whi ch depends on the alternative sigma factor RpoN (sigma (54)). Recently, a t wo-component regulatory system was identified as an element controlling tra nscription of the lipase operon. P. aeruginosa lipase is secreted via a typ e II pathway. The cytoplasmic prelipase contains a 26 amino acid N-terminal signal sequence mediating secretion across the inner membrane via the Sec- machinery. In the periplasm, lipase folds into an enzymatically active conf ormation assisted by its specific intermolecular chaperone Lif and by unspe cific accessory folding catalysts including Dsb-proteins which catalyze the formation of a disulfide bond. Enzymatically active and secretion-competen t lipase is finally transported through a complex secretion machinery consi sting of 12 different Xcp-proteins of which XcpQ forms a pore-like structur e in the outer membrane allowing the release of lipase into the extracellul ar medium. Biotechnologically important Lipases from Burkholderia glumae an d P. alcaligenes also use such a type II secretion pathway whereas lipases from P. fluorescens and Serratia marcescens, which lack a typical signal se quence are secreted via a type I pathway. Future challenges to produce Pseu domonas lipases may include artificial up-regulation of lipase gene transcr iption and construction of more efficient expression strains in which both folding and secretion of lipase are optimized. (C) 2000 Societe francaise d e biochimie et biologie moleculaire / Editions scientifiques et medicales E lsevier SAS.