J. Hermoso et al., LIPASE ACTIVATION BY NONIONIC DETERGENTS - THE CRYSTAL-STRUCTURE OF THE PORCINE LIPASE-COLIPASE-TETRAETHYLENE GLYCOL MONOOCTYL ETHER COMPLEX, The Journal of biological chemistry, 271(30), 1996, pp. 18007-18016
The crystal structure of the ternary porcine lipase-colipase-tetra eth
ylene glycol monooctyl ether (TGME) complex has been determined at 2.8
Angstrom resolution, The crystals belong to the cubic space group F23
with a = 289.1 Angstrom and display a strong pseudo-symmetry correspo
nding to a P23 lattice, Unexpectedly, the crystalline two-domain lipas
e is found in its open configuration, This indicates that in the prese
nce of colipase, pure micelles of the nonionic detergent TGME are able
to activate the enzyme; a process that includes the movement of an N-
terminal domain loop (the flap), The effects of TGME and colipase have
been confirmed by chemical modification of the active site serine res
idue using diisopropyl p-nitrophenylphosphate (E600), In addition, the
presence of a TGME molecule tightly bound to the active site pocket s
hows that TGME acts as a substrate analog, thus possibly explaining th
e inhibitory effect of this nonionic detergent on emulsified substrate
hydrolysis at submicellar concentrations, A comparison of the lipase-
colipase interactions between our porcine complex and the human-porcin
e complex (van Tilbeurgh, H., Egloff, M.-P., Martinez, C., Rugani, N.,
Verger, R., and Cambillau, C. (1993) Nature 362, 814-820) indicates t
hat except for one salt bridge interaction, they are conserved, Analys
is of the superimposed complexes shows a 5.4 degrees rotation on the r
elative position of the N-terminal domains excepting the flap that mov
es in a concerted fashion with the C-terminal domain, This flexibility
may be important for the binding of the complex to the water-lipid in
terface.