Role Of The Lid Hydrophobicity Pattern In Pancreatic Lipase Activity

Pancreatic lipase is a soluble globular protein that must undergo structural
modifications before it can hydrolyze oil droplets coated with bile salts. The
binding of colipase and movement of the lipase lid open access to the active
site. Mechanisms triggering lid mobility are unclear. The *KNILSQIVDIDGI*
fragment of the lid of the human pancreatic lipase is predicted by molecular
modeling to be a tilted peptide. Tilted peptides are hydrophobicity motifs
involved in membrane fusion and more globally in perturbations of
hydrophobic/hydrophilic interfaces. Analysis of this lid fragment predicts no
clear consensus of secondary structure that suggests that its structure is not
strongly sequence determined and could vary with environment. Point mutations
were designed to modify the hydrophobicity profile of the [240-252] fragment and
their consequences on the lipase-mediated catalysis were tested. Two mutants, in
which the tilted peptide motif was lost, also have poor activity on bile
salt-coated oil droplets and cannot be reactivated by colipase. Conversely, one
mutant in which a different tilted peptide is created retains colipase
dependence. These results suggest that the tilted hydrophobicity pattern of the
[240-252] fragment is neither important for colipase binding to lipase, nor for
interfacial binding but is important to trigger the maximal catalytic efficiency
of lipase in the presence of bile salt.