Domain-structure analysis of recombinant rat hormone-sensitive lipase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Hormone-sensitive lipase (HSL) is crucial for lipid metabolism and energy homeostasis by releasing fatty acids from triglycerides.
• Lipases share the alpha/beta-hydrolase fold and a catalytic triad, common to esterases.
• Previous sequence alignments of HSL and Moraxella TA144 lipase 2 were extended to propose HSL's catalytic triad and fold sites.

Purpose of the Study:

• To investigate the proposed domain structure of HSL.
• To determine if HSL possesses distinct catalytic and regulatory domains.
• To characterize the enzymatic properties of purified recombinant HSL.

Main Methods:

• Extended sequence alignments of HSL and Moraxella TA144 lipase 2.
• Overexpression and purification of rat HSL using a baculovirus/insect-cell system.
• Purification involved detergent solubilization, anion-exchange, and hydrophobic-interaction chromatography.
• Enzyme characterization via denaturation (guanidine hydrochloride) and limited proteolysis.

Main Results:

• Purified recombinant rat HSL (>99% purity) exhibited identical specific activity, substrate specificity, and kinase substrate ability to native HSL.
• Denaturation and proteolysis differentially affected activity against lipid-stabilized versus water-soluble substrates.
• This suggests a separation of hydrolytic activity from lipid substrate recognition.

Conclusions:

• The results support the hypothesis that HSL comprises at least two major structural domains.
• One domain likely possesses catalytic activity, while another is involved in lipid substrate recognition.
• This domain organization is key to HSL's function in lipid metabolism.