β5′ Loop of turkey pancreatic lipase: Involvement in the resistance to interfacial denaturation

Abstract

β5′ Loop is a hydrophobic loop in the C‐terminal domain of pancreatic lipases playing an important role in the interaction with lipid–water interface. The turkey pancreatic lipase (TPL) β5′ loop N404, S406, and V408 residues were mutated to Y, N, and I, respectively, to replace TPL β5′ loop by those of human pancreatic lipase (HPL), which denatures rapidly in the tributyrin–water interface, in order to investigate the involvement of theses β5′ loop residues in the pancreatic lipases interfacial stability. TPL Mut β5′ was expressed in Pichia pastoris, the mutated enzyme was purified and interfacial properties study showed that TPL Mut β5′ interfacial denaturation was faster than that of wild type TPL, which is resistant to interfacial denaturation unlike many pancreatic lipases such as HPL. TPL Mut β5′ activity in the absence of tension‐active reagents was clearly lower than that of TPL. This decreased activity was more pronounced at high temperatures. Thus mutations (N404‐Y, S406‐N, and V408‐I) introduced in the TPL β5′ loop changed the TPL behavior at tributyrin–water interface to be similar to HPL. These TPL β5′ loop residues could be responsible for the TPL interfacial stability at high temperatures and in the absence of bile‐salts.Practical applications: In contrast to classical pancreatic lipases, turkey pancreatic lipase has a high stability at the lipid‐water interface and this property makes it suitable for detergency applications. Here we have studied the β5′ loop residues responsible for the interfacial stability.(A) Surface pressure–activity profiles of TPL and TPL Mut β5′ measured on 1,2‐sn‐dicaprin. Assays were carried out at 37°C in a “zero‐order” trough (volume, 130 mL; surface area, 120 cm2). Buffer: 10 mM Tris–HCl, pH 8.0, 150 mM NaCl, 21 mM CaCl2, and 1 mM EDTA. Activities are expressed as the number of moles of substrate hydrolyzed by unit time and unit surface of the reaction compartment of the “zero‐order” trough for an arbitrary lipase concentration of 1 M. (B) Hydrolysis kinetics of 1,2‐sn‐dicaprin by TPL and TPL Mut β5′ at 37°C and at a surface pressure of 5 mN/m. Each experiment was performed in duplicate and no significant difference was observed.