Probing Conformational Changes and Interfacial Recognition Site of Lipases With Surfactants and Inhibitors

Structural studies on lipases by X-ray crystallography have revealed conformational changes occurring in the presence of surfactants/inhibitors and the pivotal role played by a molecular "lid" of variable size and structure depending on the enzyme. Besides controlling the access to the enzyme active site, the lid is involved in lipase activation, formation of the interfacial recognition site (IRS), and substrate docking within the active site. The combined use of surfactants and inhibitors has been critical for a better understanding of lipase structure-function relationships. An overview of crystal structures of lipases in complex with surfactants and inhibitors reveals common structural features and shows how surfactants monomers interact with the lid in its open conformation. The location of surfactants, inhibitors, and hydrophobic residues exposed upon lid opening provides insights into the IRS of lipases. The mechanism by which surfactants promote the lid opening can be further investigated in solution by site-directed spin labeling of lipase coupled to electron paramagnetic resonance spectroscopy. These experimental approaches are illustrated here by results obtained with mammalian digestive lipases, fungal lipases, and cutinases.