Cation-pi interaction revealed by crystal structure of thermoalkalophilic lipase: relationship between enzymatic activity and alkali metal cation

Department of Materials Chemistry, Osaka University* Enzyme and Microbial Research Technology, University Putra Malasia, Malaysia**
â—‹Hiroyoshi Matsumura* Takahiko Yamamoto* Leow Thean Chor** Abu Bakar Salleh** Tsuyoshi Inoue* Yasushi Kai* Raja Noor Zaliha Raja Abdul Rahman**

Cation-pi interactions are noncovalent binding forces that occur between cations and electron-rich orbitals of an aromatic ring. The interactions are increasingly recognized to play a dominant role in various molecular functions in chemistry and biology.
An extracellular lipase from Geobacillus zalihaii sp. strain T1 (T1 lipase) is a thermoalkalophilic enzyme that was isolated from Palm Oil Effluent (POE) in Malaysia. This enzyme is a secreted protein, which can catalyze the hydrolysis of long-chain triglycerides into fatty acids and glycerol at the interface between water and insoluble substrate at high temperature. Since POE contains high concentration of potassium ion, T1 lipase has the potential to catalyze the reaction under non-natural condition such as high concentration of potassium ion.
Herein, we have crystallized T1 lipase from Geobacillus zalihaii sp in presence of alkali metal cation (sodium and potassium ions), and have solved the crystal structure of T1 lipase at 1.5 Å resolution. The high resolution structure showed that an alikali metal cation was bound via cation-pi system in the vincinity of active site. Based on these observations, the enzymatic activity has been investigated under the buffer containing sodium and potassium ions. We will address the details of coordination structure of alkali metal cation and propose its enhanced mechanism.