The gene encoding a thermostable lipase secreted by Bacillus stearothermophilus P1 has been cloned and overexpressed in Escherichia coli. The recombinant lipase was purified to homogeneity using ammonium sulfate precipitation, anion-exchange chromatography (Poros 20 HQ) and Sephacryl S-200HR. The molecular mass was shown to be 43 209 Da by mass spectrometry. Crystals suitable for X-ray diffraction analysis were obtained by the hanging-drop method of vapour diffusion with ammonium sulfate as the precipitating agent. Determination of the structure by molecular replacement with existing mesophilic lipase structures has proved unrewarding, as there is less than 20% sequence identity with known lipase structures, but preliminary results with heavy-atom soaking indicate that this strategy will allow the structure to be solved. The availability of this new lipase structure will be of particular significance because it will be the first thermostable lipase to be described.
We describe the first lipase structure from a thermophilic organism. It shares less than 20% amino acid sequence identity with other lipases for which there are crystal structures, and shows significant insertions compared with the typical alpha/beta hydrolase canonical fold. The structure contains a zinc-binding site which is unique among all lipases with known structures, and which may play a role in enhancing thermal stability. Zinc binding is mediated by two histidine and two aspartic acid residues. These residues are present in comparable positions in the sequences of certain lipases for which there is as yet no crystal structural information, such as those from Staphylococcal species and Arabidopsis thaliana. The structure of Bacillus stearothermophilus P1 lipase provides a template for other thermostable lipases, and offers insight into mechanisms used to enhance thermal stability which may be of commercial value in engineering lipases for industrial uses.
Representative scheme of Bacterial_lip_FamI.5 structure and an image from PDBsum server
Databases
PDB-Sum
1JI3 Previously Class, Architecture, Topology and Homologous superfamily - PDB-Sum server
FSSP
1JI3Fold classification based on Structure-Structure alignment of Proteins - FSSP server
