THE OPEN CONFORMATION OF A PSEUDOMONAS LIPASE

Background: The interfacial activation of lipases results primarily fr om conformational changes in the enzymes which expose the active site and provide a hydrophobic surface for interaction with the lipid subst rate, Comparison of the crystallization conditions used and the struct ures observed for a variety of lipases suggests that the enzyme confor mation is dependent on solution conditions. Pseudomonas cepacia lipase (PCL) was crystallized in conditions from which the open, active conf ormation of the enzyme was expected. Its three-dimensional structure w as determined independently in three different laboratories and was co mpared with the previously reported closed conformations of the closel y related lipases from Pseudomonas glumae (PGL) and Chromobacterium vi scosum (CVL). These structures provide new insights into the function of this commercially important family of lipases. Results: The three i ndependent structures of PCL superimpose with only small differences i n the mainchain conformations, As expected, the observed conformation reveals a catalytic site exposed to the solvent, Superposition of PCL with the PGL and CVL structures indicates that the rearrangement from the closed to the open conformation involves three loops. The largest movement involves a 40 residue stretch, within which a helical segment moves to afford access to the catalytic site. A hydrophobic cleft tha t is presumed to be the lipid-binding site is formed around the active site, Conclusions: The interfacial activation of Pseudomonas lipases involves conformational rearrangements of surface loops and appears to conform to models of activation deduced from the structures of fungal and mammalian lipases. Factors controlling the conformational rearran gement are not understood, but a comparison of crystallization conditi ons and observed conformation suggests that the conformation of the pr otein is determined by the solution conditions, perhaps by the dielect ric constant.