ROLE OF THE LIPB GENE-PRODUCT IN THE FOLDING OF THE SECRETED LIPASE OF PSEUDOMONAS-GLUMAE

The LipB protein of Pseudomonas glumae is essential for the production of active extracellular lipase encoded by the lipA gene. When lipase is overproduced in P. glumae in the absence of a functional lipB gene, the enzyme accumulates intracellularly in an inactive conformation. H eterologous expression of the lipase in Pseudomonas aeruginosa, Bacill us subtilis and Escherichia coli indicated that LipB is not directly i nvolved in the translocation of the lipase across the inner or outer m embrane. However, the presence of LipB was essential for obtaining act ive lipase and had a profound influence on the stability of the protei n to proteolytic degradation. Inactive lipase, produced in the absence of LipB could be activated in vitro by unfolding and refolding, which demonstrates that LipB activity is not responsible for an essential c ovalent modification of the enzyme. We propose that LipB is a lipase-s pecific foldase. Furthermore, proper folding of the lipase in the peri plasm appears to be essential for Xcp-mediated translocation across th e outer membrane.