“Beta-Galactosidase at the membrane-water interface: A case of an active enzyme with non-native conformation”

JULIETA M. SÁNCHEZ, ; VERÓNICA NOLAN ; MARÍA A. PERILLO.

COLLOIDS AND SURFACES B-BIOINTERFACES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 118 p. 1 - 7

0927-7765

Previously we demonstrated that E.coli beta-galactosidase (b-Gal) binds to zwitterionic lipid membranes improving its catalytic activity. To understand this activation mechanism from the protein perspective, we investigated the structure/activity relationship of b-Gal in solution and in the presence of a lipid-water interface (LWI). Thus, the thermal dependence of parameters derived from spectroscopy and calorimetry, in the presence and absence of EPC, were evaluated varying lipid and/or protein concentrations.                             In water, the unfolding of b-Gal followed the general model N4(aq)DI4(aq)D4U(aq)"Agg(aq). The first step represents the conformational change of the native oligomer, and the second step represents the dissociation of the non-native species with the concomitant unfolding strongly displaced towards the aggregation.                      In the presence of lipids, b-Gal participates in the lipid-water partition equilibrium N4(aq)DN4(lip). Similar unfolding reactions occurs in both phases but at the LWI aggregation of U(lip) is inhibited. Compared with N4(aq), N4(lip) has a more active and swollen conformation and turns into the corresponding non-native but active I4(lip) species at a lower temperature. The high lipid binding affinity of I4(aq) leads to a decrease in the U(aq) concentration and consequently its aggregation and irreversible inactivation. b-Gal bound at the LWI behaves as an active molten globule-like enzyme.