Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Nicot, C.; Vacher, Monique; Vincent, Michel; Gallay, Jacques; Waks, Marcel

doi:10.1021/bi00345a041

Cited by 90 publications

(76 citation statements)

References 49 publications

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“…At a low degree of complexity, reverse micelles constitute a good membrane-mimetic system (Nicot et al, 1985;Leodidis and Hatton, 1990) for the study of the complex physicochemical forces acting at interfaces of multicomponent assemblies (Israelachvili and McGuiggan, 1988). The large size (66.5 kDa) and the number of amino acids (585) in HSA provide the opportunity for multiple protein-micellar surface interactions which would contribute to the process of conformational changes described herein.…”

Section: Discussionmentioning

confidence: 99%

“…The reaction of N-bromosuccinimide with Trp214 was carried out in aqueous and micellar solutions as previously described by Nicot et al (1985). The course of tryptophan oxidation reaction was followed by the decrease in fluorescence emission (Privat et a1.,1976).…”

Section: Chemical Modifications Of Albuminmentioning

confidence: 99%

“…Because the anisotropic and amphipatic nature of biological membranes is preserved to a large extent by the reverse micellar system (Nicot et al, 1985) the very large interfacial surface generated by the reverse micellar system is expected to amplify such effects.…”

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confidence: 99%

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Ligand binding at membrane mimetic interfaces

Desfosses¹,

Cittanova²,

Urbach³

et al. 1991

European Journal of Biochemistry

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Chemical Modifications Of Albuminmentioning

confidence: 99%

See 1 more Smart Citation

Ligand binding at membrane mimetic interfaces

Desfosses¹,

Cittanova²,

Urbach³

et al. 1991

European Journal of Biochemistry

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“…The polar heads of the surfactant molecules are directed toward the interior of a water-containing sphere, whereas the aliphatic tails are oriented toward the non-polar organic phase. The water structure within the reverse micelles may resemble that of water adjacent to biological membranes (Boicelli et al 1982), and it has been suggested that the reverse micellar system reliably mimics the microenvironment that enzymes encounter in the intracellular milieu (Nicot et al 1985, Luisi et al 1988, O'Connor and Wiggins 1988, Faeder and Ladanyi 2000.…”

Section: Introductionmentioning

confidence: 99%

Reverse micelles in organic solvents: a medium for the biotechnological use of extreme halophilic enzymes at low salt concentration

Marhuenda-Egea

Piera-Velázquez

Cadenas

et al. 2002

Archaea

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Summary Alkaline p-nitrophenylphosphate phosphatase ( pNPPase) from the halophilic archaeobacterium Halobacterium salinarum (previously halobium) was solubilized at low salt concentration in reverse micelles of hexadecyltrimethylammoniumbromide in cyclohexane with 1-butanol as cosurfactant. The enzyme maintained its catalytic properties under these conditions. The thermodynamic "solvation-stabilization hypothesis" has been used to explain the bell-shaped dependence of pNPPase activity on the water content of reverse micelles, in terms of protein-solvent interactions. According to this model, the stability of the folded protein depends on a network of hydrated ions associated with acidic residues at the protein surface. At low salt concentration and low water content (the ratio of water concentration to surfactant concentration; w 0 ), the network of hydrated ions within the reverse micelles may involve the cationic heads of the surfactant. The bell-shaped profile of the relationship between enzyme activity and w 0 varied depending on the concentrations of NaCl and Mn 2+.

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“…At first glance, it might be expected that the enzyme would be more active in water with properties closer to those found in the surface of membranes. The extrinsic membranous myelin basic protein, for example, is preferentially solubilized in bound water (Nicot et al, 1985). The fact that the El conformer and, hence, the enzymatic turnover, needs bulk water, suggests that the catalytic site in that conformation is shielded from the membranous surface, either in the interior of the protein or projected to the cytoplasmic portion of the enzyme.…”

Section: Discussionmentioning

confidence: 99%

Are there different water requirements in different steps of a catalytic cycle?

Barrabin

Scofano

Gómez‐Puyou

et al. 1993

European Journal of Biochemistry

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The Ca2+-ATPase from sarcoplasmic reticulum was transferred in an active form to a low-water system composed of toluene, phospholipids, and Triton X-100 (TPT). The Ca2+-ATPase activity in the TPT system with 4.0% water (by vol.) was about 50% of the activity observed in all-aqueous mixtures. Phosphate formation was linear with time up to 20% of ATP hydrolysis and, as expected from an enzyme-catalysed reaction, activity was linear with protein concentration. No ATPase activity was detected in the presence of 3 mM EGTA, indicating that the enzyme retained its Ca2+ dependence in the TPT system. A hyperbolic response to ATP concentration was observed with a K , of 0.15 mM. There was no detectable ATPase activity at water concentrations below 1.5% (by vol.). With 2.0% water, activity became detectable and increased as the water content was progressively raised to 7.0% (by vol.). Higher amounts of water produced unstable emulsions. Enzyme phosphorylation by ATP and dephosphorylation took place in the TPT system. The velocities of both enzyme phosphorylation and dephosphorylation increased with increments in the water content. The enzyme could also be phosphorylated in the TPT system by inorganic phosphate. However, in comparison to ATP, phosphorylation by phosphate took place with significantly lower amounts of water. It is suggested that at low amounts of water, the enzyme is in a relatively rigid conformation and, as the water content is increased, the ATPase acquires more flexibility and, hence, the capacity to carry out catalysis at higher rates. Nevertheless, the release of conformational constraints of the catalytic site of the E, conformer takes place at water concentrations much lower than those needed for the expression of catalytic activity by the E, conformer.A considerable amount of work has accumulated on the behavior of enzymes in systems formed predominantly with organic solvents. The studies have been carried out with enzymes dispersed in the solvent (Klibanov, 1983(Klibanov, , 1989 or entrapped in the interior of reverse micelles (Martinek et al., 1986;Luisi and Magid, 1986;Walde et al., 1990). One of the salient features of enzymes in either of the two conditions is that, when they are in contact with low amounts of water, they exhibit a high thermostability (Garza-Ramos et al., 1989; Ayala et al., 1986; Zacks and Klibanov, 1984, 1988;Wheeler and Croteau, 1986) and low catalytic rates (GarzaRamos et al., 1989(GarzaRamos et al., , 1990(GarzaRamos et al., , 1992a. It has been proposed that these two phenomena result from restrictions in enzyme conformational mobility as imposed by the low-water environment (for review see Garza-Ramos et al., 199213 mational changes, it should be possible to stabilize particular enzyme conformations by varying the amount of water in contact with the enzyme. Studies along this line could also shed light on solvent-protein interactions that occur during catalysis, in particular if different steps of the catalytic cycle have distinct and defined water requeriments. The ...

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Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Cited by 90 publications

References 49 publications

Ligand binding at membrane mimetic interfaces

Ligand binding at membrane mimetic interfaces

Reverse micelles in organic solvents: a medium for the biotechnological use of extreme halophilic enzymes at low salt concentration

Are there different water requirements in different steps of a catalytic cycle?

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