This work explores the role of one of the factors explaining lipase/esteras
e activity: the contribution of electrostatic interactions to lipase/estera
se activity. The electrostatic potential distribution on the molecular surf
ace of an enzyme as a function of pH determines, to a large extent, the enz
yme's pH activity profile. Other important factors include the presence and
distribution of polar and hydrophobic residues in the active cleft. We hav
e mapped the electrostatic potential distribution as a function of pH on th
e molecular surface of nine lipases/esterases for which the 3D structure is
experimentally known. A comparison of these potential maps at different pH
values with the corresponding pH-activity profile, pH optimum or pH range
where the activity displayed by the enzyme is maximum, has revealed a consi
derable correlation. A negative potential in the active site appears correl
ated with maximum activity towards triglycerides, which has prompted us to
propose a model for product release ('The electrostatic catapult model') af
ter cleavage of an ester bond. At the same time as the bottom of the active
site cleft becomes negatively charged, other nearby regions also titrate a
nd become negatively charged when pH becomes more alkaline, for some of the
studied lipases. If such lipases also show phospholipase activity (such as
guinea pig lipase-related proteins 2 chimera) we raise the hypothesis that
such other titratable regions after becoming negatively charged might stab
ilise the positive charge present in the polar head of phospholipids, such
as phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine. Th
e distribution of polar, weak polar and non-polar residues on the molecular
surface of each studied lipase, in particular the active site region, was
compared for all the lipases studied. The combination of graphical visualis
ation of the electrostatic potential maps and the polarity maps combined wi
th knowledge about the location of key residues on the protein surface allo
ws us to envision atomic models for lipolytic activity. (C) 2001 Elsevier S
cience B.V. All rights reserved.