Aim: To understand the details of the action of fungal lipase and the mechanism for its observed
Background: Fungal lipase, crucial to biotechnology, functions at the lipid - water interface where it
undergoes a poorly understood interfacial activation. Biochemical factors influencing its activation
and inhibition are also poorly understood. This study provides a basis for its activity and a plausible
mechanism for interfacial activation.
Objective: To determine the structures of fungal lipase in different crystal forms in complex with
their enzymatic reactants and inhibitors.
Methods: X-ray crystallography.
Results: Thermomyces lanuginosa lipase was visualized in three crystal forms, of space groups H32,
P21 and I222 at 1.3 to 1.45 Å resolution. Rhombohedral crystals have one molecule, lacking segment
241 to 252, as an asymmetric unit, with molecules organized as two trimers. Monoclinic crystals’
asymmetric unit is six intact molecules organized as two, nearly identical trimers, each exhibiting an
NCS threefold axis. The “lid” helix was consistently closed. Oligomerization into trimers creates an
internal hydrophobic cavity where catalysis occurs. In monoclinic and orthorhombic crystals, active
site serines were esterified to fatty acids. Lipase had bound within their trimeric, hydrophobic cavities
1,3-diacylglycerols with fatty acid chain lengths of about 18 carbons.
Conclusion: Results suggest trimers are likely the active form of the enzyme at the lipid-water interface.
Formation of trimers may provide an explanation for “interfacial activation”.