|
Cutinases, a group of cutin degrading enzymes with molecular masses of around
22-25 kDa (Kolattukudy, 1984), are also able to efficiently hydrolyse
triglycerides (De Geus et al., 1989; Lauwereys et al., 1991), but without
exhibiting the interfacial activation phenomenom (Sarda et al., 1958). They
belong to a class of proteins with a common structural framework, called the
alpha/beta hydrolase fold (Martinez et al., 1992; Ollis et al., 1992). We
describe herein the structure of cutinase covalently inhibited by
diethyl-p-nitrophenyl phosphate (E600) and refined at 1.9-A resolution. Contrary
to what has previously been reported with lipases (Brzozowski et al., 1991;
Derewenda et al., 1992; Van Tilbeurgh et al., 1993), no significant structural
rearrangement was observed here in cutinase upon the inhibitor binding.
Moreover, the structure of the active site machinery, consisting of a catalytic
triad (S120, H188, D175) and an oxyanion hole (Q121 and S42), was found to be
identical to that of the native enzyme, whereas the oxyanion hole of Rhizomucor
lipase (Brzozowski et al., 1991; Derewenda et al., 1992), like that of
pancreatic lipase (van Tilbeurgh et al., 1993), is formed only upon
enzyme-ligand complex formation. The fact that cutinase does not display
interfacial activation cannot therefore only be due to the absence of a lid but
might also be attributable to the presence of a preformed oxyanion hole.
|
