COMPUTATIONAL STUDIES OF THE ACTIVATION OF LIPASES AND THE EFFECT OF A HYDROPHOBIC ENVIRONMENT

We have investigated the activation pathway of three wild type lipases and three mutants using molecular dynamics techniques combined with a constrained mechanical protocol. The activation of these lipases invo lves a rigid body hinge-type motion of a single helix, which is displa ced during activation to expose the active site and give access to the substrate. Our results suggest that the activation of lipases is enha nced in a hydrophobic environment as is generally observed in experime nts. The energy gain upon activation varies between the different lipa ses and depends strongly on the distribution of the charged residues i n the activating loop region. In a low dielectric constant medium (suc h as a lipid environment), the electrostatic interactions between the residues located in the vicinity of the activating loop (lipid contact zone) are dominant and determine the activation of the lipases. Calcu lations of the pK(a)s qualitatively indicate that some titratable resi dues experience significant pK shifts upon activation. These calculati ons may provide sufficient details for an understanding of the origin and magnitude of a given electrostatic effect and may provide an avenu e for exploring the activation pathway of lipases.