Interaction of α-lactalbumin with dimyristoyl phosphatidylcholine vesicles

Herreman, W.; Tornout, Philippe Van; Cauwelaert, F.H. Van; Hanssens, Ignace

doi:10.1016/0005-2736(81)90467-3

Cited by 39 publications

(14 citation statements)

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“…This interest has lead to substantial progress in defining the effects of lipid on the physical and functional state of a-LA. Previous physical studies of a-LAhesicle mixtures have provided some valuable information on the nature and extent of interactions of various CY-LA conformations with the lipid (Hanssens et al, 1980(Hanssens et al, , 1983(Hanssens et al, , 1985Herreman et al, 1981aHerreman et al, , 1981bAmeloot et al, 1984;Berliner & Koga, 1987;Permyakov et al, 1988a). Fluorescent results with probes placed in the bilayer suggested that the lipid was not strongly perturbed upon interaction with a-LA at neutral pH, and that the association was largely electrostatic with the vesicle surface (Hanssens et al, 1980(Hanssens et al, , 1983(Hanssens et al, , 1985Herreman et al, 1981aHerreman et al, , 1981bAmeloot et al, 1984), as evidenced by the absence of an energy transfer band with a protein tryptophan (Brown, 1984).…”

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confidence: 99%

“…Previous physical studies of a-LAhesicle mixtures have provided some valuable information on the nature and extent of interactions of various CY-LA conformations with the lipid (Hanssens et al, 1980(Hanssens et al, , 1983(Hanssens et al, , 1985Herreman et al, 1981aHerreman et al, , 1981bAmeloot et al, 1984;Berliner & Koga, 1987;Permyakov et al, 1988a). Fluorescent results with probes placed in the bilayer suggested that the lipid was not strongly perturbed upon interaction with a-LA at neutral pH, and that the association was largely electrostatic with the vesicle surface (Hanssens et al, 1980(Hanssens et al, , 1983(Hanssens et al, , 1985Herreman et al, 1981aHerreman et al, , 1981bAmeloot et al, 1984), as evidenced by the absence of an energy transfer band with a protein tryptophan (Brown, 1984). On the other hand, at acidic pH (<4), it was found that protein insertion into the bilayer is pronounced, exhibiting strong protein-probe energy transfer (Herreman et al, 1981a(Herreman et al, , 1981b) and a marked tendency to solubilize the lipid into micellar complexes (Hanssens et al, 1980(Hanssens et al, , 1983Dangreau et al, 1982), suggesting that, at low pH, a-LA is an intrinsic membrane protein (Brown, 1984).…”

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Membrane‐bound states of α‐lactalbumin: Implications for the protein stability and conformation

1996

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Abstracta-Lactalbumin (a-LA) associates with dimyristoylphosphatidylcholine (DMPC) or egg lecithin (EPC) liposomes. Thermal denaturation of isolated DMPC or EPC a-LA complexes was dependent on the metal bound state of the protein. The intrinsic fluorescence of thermally denatured DMPC-a-LA was sensitive to two thermal transitions: the T,. of the lipid vesicles, and the denaturation of the protein. Quenching experiments suggested that tryptophan accessibility increased upon protein-DMPC association, in contrast with earlier suggestions that the limited emission red shift upon association with the liposome was due to partial insertion of tryptophan into the apolar phase of the bilayer (Hanssens I et al., 1985, Biochim Biophys Acta 817:154-166). On the other hand, above the protein transition (70 "C), the spectral blue shifts and reduced accessibility to quencher suggested that tryptophan interacts significantly with the apolar phase of either DMPC and EPC. At pH 2, where the protein inserts into the bilayer rapidly, the isolated DMPC-a-LA complex showed a distinct fluorescence thermal transition between 40 and 60 "C, consistent with a partially inserted form that possesses some degree of tertiary structure and unfolds cooperatively. This result is significant in light of earlier findings of increased helicity for the acid form, i.e., molten globule state of the protein (Hanssens I et al., 1985, Biochim Biophys Acta 812154-166). These results suggest a model where a limited expansion of conformation occurs upon association with the membrane at neutral pH and physiological temperatures, with a concomitant increase in the exposure of tryptophan to external quenchers; i.e., the current data do not support a model where an apolar, tryptophan-containing surface is covered by the lipid phase of the bilayer.

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confidence: 99%

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Membrane‐bound states of α‐lactalbumin: Implications for the protein stability and conformation

1996

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“…␣LA is able to interact with lipid bilayers (13,14) and provides a suitable model to characterize the structural transition involved in membrane association of water-soluble proteins, since its conformational properties have been extensively studied (15,16). Moreover, the possibility of trapping stable reduction intermediates of this protein offers the opportunity to follow the conformational changes associated with binding of different folding intermediates to membranes (16,17).…”

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Binding of Molten Globule-like Conformations to Lipid Bilayers

Bañuelos

Muga

1995

Journal of Biological Chemistry

114

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The effect of membrane binding on the structure and stability of several conformers of ␣-lactalbumin was studied by infrared spectroscopy, circular dichroism, and fluorescence spectroscopy. In solution, under experimental conditions where all conformers interact with negatively charged membranes, they show significant conformational differences. However, binding to negatively charged membranes, which causes considerable changes in the structure of these conformers, leads to a remarkably similar protein conformation. The membrane-associated conformations are characterized by 1) a high helical content, greater than any of those found in solution, 2) a lack of stable tertiary structure, and 3) the disappearance of their thermotropic transition. These observations indicate that association with negatively charged membranes induces a conformational change within ␣-lactalbumin to a flexible, molten globule-like state.

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“…The effects can be mediated via changes in the membrane proteins [2,21,36,37] or in the lipid bilayer [18,35,52]. While the effect on protein structure is specific for each case, the presumed effect on the lipid bilayer should be more general and less specific.…”

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confidence: 99%

Increase in lipid microviscosity of unilamellar vesicles upon the creation of transmembrane potential

1982

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Diffusion potential of potassium ions was found in unilamellar vesicles of phosphatidyl choline. The vesicles, which included potassium sulfate buffered with potassium phosphate were diluted into an analogous salt solution made of sodium sulfate and sodium phosphate. The diffusion potential was created by the addition of the potassium-ionophore, valinomycin. The change in lipid microviscosity, ensuing the formation of membrane potential, was measured by the conventional method of fluorescence depolarization with 1,6-diphenyl-1,3,5-hexatriene as a probe. Lipid microviscosity was found to increase with membrane potential in a nonlinear manner, irrespective of the potential direction. Two tentative interpretations are proposed for this observation. The first assumes that the membrane potential imposes an energy barrier on the lipid flow which can be treated in terms of Boltzmann-distribution. The other interpretation assumes a decrease in lipid-free volume due to the pressure induced by the electrical potential. Since increase in lipid viscosity can reduce lateral and rotational motions, as well as increase exposure of functional membrane proteins, physiological effects induced by transmembrane potential could be associated with such dynamic changes.

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Interaction of α-lactalbumin with dimyristoyl phosphatidylcholine vesicles

Cited by 39 publications

References 31 publications

Membrane‐bound states of α‐lactalbumin: Implications for the protein stability and conformation

Membrane‐bound states of α‐lactalbumin: Implications for the protein stability and conformation

Binding of Molten Globule-like Conformations to Lipid Bilayers

Increase in lipid microviscosity of unilamellar vesicles upon the creation of transmembrane potential

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