Ligand binding at membrane mimetic interfaces

Abstract

The behaviour of human serum albumin in the presence of three chemically distinct ligands: oxyphenylbutazone, dansylsarcosine and hemin, has been compared in buffer and in reverse micelles of isooctane, water, and either sodium bis(2-ethylhexyl)sulfosuccinate or hexadecyl trimethylammonium bromide, systems selected to mimic the membrane-water interface. Upon micellar incorporation, the dansylsarcosine-albumin complex dissociated, as evidenced by fluorescence emission spectroscopy (red shift from 485 nm to 570 nm) and by fluorescence polarization measurements. In contrast, the hemin-albumin complex remained stable in reverse micelles, as judged from the Soret absorption band at 408 nm and the molar absorption coefficient of 8.4 x lo4 M -' cm-'. The oxyphenylbutazone to albumin binding curves reveal that while the association constant remained unchanged ( K , 1.0 x lo5 M-'), only a fraction of the albumin molecules present reacted with the ligand. The results were unaffected by the nature and the concentration of the surfactant.These findings can be interpreted in the light of conformational changes induced in human serum albumin by the large micellar inner surface area. The blue shift of the fluorescence emission maximum from 344nm in buffer to 327 nm in sodium bis(2-ethylhexyl)sulfosuccinate micelles and the lesser reactivity/accessibility of the fluorophore to oxidation by N-bromosuccinimide, indicate perturbations of the sole tryptophan-214 microenvironment. However, the distance between the indole residue and tyrosine-41 1 does not seem substantially modified by the 15% decrease affecting the CI helices of the albumin molecule. It is proposed that the results reported herein reflect the interactions of albumin with a membrane-like interface which generates two protein subpopulations differing in their membrane-surface and ligand affinities. Overall and local conformational changes, originating from this surface-induced effect, may thus constitute a ligand-release facilitating mechanism acting at cellular membrane levels.

Proteins as Invited Guests of Reverse Micelles: Conformational Effects, Significance, Applications

“…attributed to a denaturation rnechanism. The problem \VUS in fact 1l10re complex as shO\VI1 later by the work of Desfosses et al (1991). These investigators found indeed a loss of intensity in both the near (not sho\vn) and the far-ultraviolet regions of the albuluin CD spectruIIl (Figure 14).…”

Mechanism of protein extraction from the solid state by water-in-oil microemulsions

“…The difference in binding is much too large to be attributed to the difference in molecular size of BSA relative to CHY and LYS. In addition, others have observed strong interaction between AOT and albumin (Desfosses et al, 1991;Marzola et al, 1991;Takeda et al, 1994). Second, the fit of the isotherm to the data in Figure 5 is poor relative to the data for CHY and LYS.…”

“…Of interest, a recent report suggests that in the w o range 15-30 CHY solubilizes into w/o-MEs as dimers (Oldfield et al, 1996). However, the solubilization of either bovine or human serum albumin increases w/o-ME size (Desfosses et al, 1991;Takeda et al, 1994). Concerning LYS, a recent quasielastic light scattering study reports that its presence increased the size of w/o-MEs; however, their results did not take into account the contribution of interdroplet attractions occurring at the AOT concentration they employed (100 mM) to the measured scattered intensity (Chang et al, 1994).…”

“…This may indicate mass-transfer limitations during the adsorption process or differences in binding due to reorganization of BSA-AOT-water complex after its formation. Moreover, the secondary structure of albumin is reported to change strongly upon binding with AOT (Desfosses et al, 1991;Marzola et al, 1991;Takeda et al, 1994). This change in structure may lead to an alteration in the adsorption behavior.…”

Bovine serum albumin with glycated carboxyl groups shows membrane-perturbing activities

“…Previous studies revealed that BSA can transfer lipid amphiphile to the lipid bilayer membranes [6], reflecting that BSA could exert its function at the lipid-water interface. Moreover, several studies have suggested that membrane-interface or membrane-mimicking surface induces conformational changes in human serum albumin [7][8][9]. Taken together, these findings suggest that serum albumin could interact with the lipid bilayers.…”