Specificity of the lipase-specific foldases of gram-negative bacteria and the role of the membrane anchor

Folding of lipases that are secreted by Pseudomonads and other gram-negativ e bacteria via the type II secretion pathway is facilitated by dedicated ch aperones, called lipase-specific foldases (Lifs). Lifs are membrane-anchore d proteins with a large periplasmic domain. The functional interaction betw een the Lif and its cognate lipase is specific, since the Pseudomonas aerug inosa Lif was found not to substitute for Lifs from Burkholderia glumae or Acinetobacter calcoaceticus. However, the P. aeruginosa Lif was able to act ivate the lipase from the closely related species P. alcaligenes. Hybrid pr oteins constructed from parts of the P. aeruginosa and B. glumae Lifs revea led that the C-terminal 138 amino acids of the B. glumae Lif determine the specificity of the interaction with the cognate lipase. Furthermore, the pe riplasmic domain of the B. glumae Lif was functional when cloned in frame w ith a cleavable signal sequence, which demonstrates that the membrane ancho r is not essential for Lif function in vivo. However, the recombinant Lif w as released into the medium, indicating that the function of the membrane a nchor is to prevent secretion of the Lif together with the lipase.