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Authors
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B.Sias,
F.Ferrato,
P.Grandval,
D.Lafont,
P.Boullanger,
A.De Caro,
B.Leboeuf,
R.Verger,
F.Carrière.
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Human pancreatic lipase-related protein 2 (HPLRP2) was found to be expressed in
the pancreas, but its biochemical properties were not investigated in detail. A
recombinant HPLRP2 was produced in insect cells and the yeast Pichia pastoris
and purified by cation exchange chromatography. Its substrate specificity was
investigated using pH-stat and monomolecular film techniques and various lipid
substrates (triglycerides, diglycerides, phospholipids, and galactolipids).
Lipase activity of HPLRP2 on trioctanoin was inhibited by bile salts and poorly
restored by adding colipase. In vivo, HPLRP2 therefore seems unlikely to show
any lipase activity on dietary fat. In human pancreatic lipase (HPL), residues
R256, D257, Y267, and K268 are involved in the stabilization of the open
conformation of the lid domain, which interacts with colipase. These residues
are not conserved in HPLRP2. When the corresponding mutations (R256G, D257G,
Y267F, and K268E) are introduced into HPL, the effects of colipase are
drastically reduced in the presence of bile salts. This may explain why colipase
has such weak effects on HPLRP2. HPLRP2 displayed a very low level of activity
on phospholipid micelles and monomolecular films. Its activity on
monogalactosyldiglyceride monomolecular film, which was much higher, was similar
to the activity of guinea pig pancreatic lipase related-protein 2, which shows
the highest galactolipase activity ever measured. The physiological role of
HPLRP2 suggested by the present results is the digestion of galactolipids, the
most abundant lipids occurring in plant cells, and therefore, in the vegetables
that are part of the human diet.
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