The gene coding for a novel cold-active esterase PMGL3 was previously obtained from a Siberian permafrost metagenomic DNA library and expressed in Escherichia coli. We elucidated the 3D structure of the enzyme which belongs to the hormone-sensitive lipase (HSL) family. Similar to other bacterial HSLs, PMGL3 shares a canonical alpha/beta hydrolase fold and is presumably a dimer in solution but, in addition to the dimer, it forms a tetrameric structure in a crystal and upon prolonged incubation at 4 degreesC. Detailed analysis demonstrated that the crystal tetramer of PMGL3 has a unique architecture compared to other known tetramers of the bacterial HSLs. To study the role of the specific residues comprising the tetramerization interface of PMGL3, several mutant variants were constructed. Size exclusion chromatography (SEC) analysis of D7N, E47Q, and K67A mutants demonstrated that they still contained a portion of tetrameric form after heat treatment, although its amount was significantly lower in D7N and K67A compared to the wild type. Moreover, the D7N and K67A mutants demonstrated a 40 and 60% increase in the half-life at 40 degreesC in comparison with the wild type protein. K(m) values of these mutants were similar to that of the wt PMGL3. However, the catalytic constants of the E47Q and K67A mutants were reduced by ~40%.
Representative scheme of Hormone-sensitive_lipase_like structure and an image from PDBsum server
Databases
PDB-Sum
7B1X Previously Class, Architecture, Topology and Homologous superfamily - PDB-Sum server
FSSP
7B1XFold classification based on Structure-Structure alignment of Proteins - FSSP server
