INTERFACIAL ACTIVATION OF THE LIPASE PROCOLIPASE COMPLEX BY MIXED MICELLES REVEALED BY X-RAY CRYSTALLOGRAPHY

The three-dimensional structure of the lipase-procolipase complex, co- crystallized with mixed micelles of phosphatidylcholine and bile salt, has been determined at 3 angstrom resolution by X-ray crystallography . The lid, a surface helix covering the catalytic triad of lipase, ado pts a totally different conformation which allows phospholipid to bind to the enzyme's active site. The open lid is an essential component o f the active site and interacts with procolipase. Together they form t he lipid-water interface binding site. This reorganization of the lid structure provokes a second drastic conformational change in an active site loop, which in its turn creates the oxyanion hole (induced fit).