The surface charge of apolipoproteins, phospholipid liposomes, and human very low density lipoproteins.

Heuck, C C; Daerr, W; Haberbosch, Werner; Horn, D.; Lüddecke, Erik

doi:10.1016/s0021-9258(20)82067-5

Cited by 9 publications

(4 citation statements)

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“…R5500), Germany, and used without further purification. It has a net charge of about +4 at pH 7 resulting from 10 acidic residues (Asp, Glu) and 18 basic residues (Lys, Arg, His) . The nonpolar fraction of the water-accessible surface area is in the range 46–50%. , Urea was obtained from Fluka, and glycerol from Merck.…”

Section: Methodsmentioning

confidence: 99%

“…44 The isoelectric point (pI) of RNase A is 9.6 so that it exposes a positive net charge at pH values below the pI, e.g., a net charge of about +4 at pH 7. 30 The point of zero charge (PZC) of the silica surface of the mesoporous materials is just below 3. Hence, the unmodified host surface is negatively charged at pH values above 3.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Stability, Hydration, and Thermodynamic Properties of RNase A Confined in Surface-Functionalized SBA-15 Mesoporous Molecular Sieves

et al. 2014

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Mesoporous silicates (MPS) have several advantages for the immobilization of enzymes and large organic molecules. They possess well-defined pores and their surfaces can be functionalized by chemical methods. In this study, the model protein ribonuclease A (RNase A) was encapsulated in unmodified amino- and carboxy-functionalized rodlike SBA-15 with pore widths ranging from 4.0 to 5.8 nm. Differential scanning (DSC) and pressure perturbation (PPC) calorimetric techniques were employed to evaluate the stability, hydration, and volumetric properties of the confined protein. In addition, the influence of the solution pH, the surface functionalization, and cosolvents on the protein immobilization and the thermal stability of the immobilized protein are reported. The extent of stabilization depends strongly on the surface characteristics of the host, such as the charge density, and on geometric parameters, i.e., the pore size and pore volume. The addition of the chaotropic agent urea leads to an increased protein loading. Addition of the kosmotropic agent glycerol has the opposite effect. The stability of the protein RNase A confined in all the mesoporous silicates is drastically enhanced and is of the order of ΔT m ≈ 30 ± 10 °C regarding the increase in temperature stability. The highest immobilization capacity, fastest immobilization rate, and maximum thermal stability was achieved for the surface-functionalized SBA-15-COOH. The increased temperature stability is probably not only due to the entropy-driven excluded volume effect but also due to an increased hydration strength of the protein within the narrow silica pores, similar to the effects compatible osmolytes impose on protein hydration and stability. The absence of an expansivity increase of the confined protein after thermal denaturation indicates that inside the pores complete unfolding of the protein is not feasible anymore.

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Section: Methodsmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Stability, Hydration, and Thermodynamic Properties of RNase A Confined in Surface-Functionalized SBA-15 Mesoporous Molecular Sieves

et al. 2014

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“…This is a crude approximation, since apo A-I dimers are not spheres and do not have a symmetrical change distribution. We assumed that the net charge of an apo A-I dimer at pH 7.6 was -8 as inferred from potentiometric titrations(Heuck et al, 1983) and that its radius was 15…”

mentioning

confidence: 99%

Self-association of human apolipoproteins A-I and A-II and interactions of apolipoprotein A-I with bile salts: quasi-elastic light scattering studies

Donovan¹,

Benedek²,

Carey³

1987

Biochemistry

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We employed quasi-elastic light scattering (QLS) to systematically study the aqueous self-association of human apolipoproteins A-I and A-II (apo A-I and apo A-II) and the interactions of apo A-I with common taurine-conjugated bile salts. Self-association of apo A-I was promoted by increases in apolipoprotein concentration (0.09-2.2 mg/mL) and ionic strength (0.15-2.0 M NaCl), inhibited by increases in temperature (5-50 degrees C) and guanidine hydrochloride concentration (0-2.0 M), and unaffected by hydrostatic pressures up to 500 atm. The mean hydrodynamic radius (Rh) of apo A-I micelles ranged from 38 A to a maximum asymptotic value of 68 A. We examined several possible models of apo A-I self-association; the model that best fitted the Rh values assumed that apo A-I monomers first interacted at low concentrations to form dimers, which then further associated to form ring-shaped limiting octamers. Comparison of the temperature-dependent and ionic strength dependent free energy changes for the formation of octamers from apo A-I dimers suggested that hydrophobic forces strongly favored self-association and that electrostatic repulsive forces were only weakly counteractive. Apo A-II self-association was also promoted by increases in apolipoprotein concentration (0.2-1.8 mg/mL) and inhibited by increases in guanidine hydrochloride concentration (0-1.0 M) but was unaffected by variations in temperature (10-37 degrees C): the largest Rh values observed were consistent with limiting tetramers. As demonstrated by equilibrium dialysis, bile salts in concentrations below their critical micellar concentrations (cmc) bound to apo A-I micelles but had no effect upon apo A-I self-association, as inferred from constant Rh values. When bile salt concentrations exceeded their aqueous cmc values, a dissociation of apo A-I micelles resulted with the formation of mixed bile salt/apo A-I micelles. These studies support the concepts that apo A-I and apo A-II form small dimeric micelles at low concentrations that grow sharply to reach limiting sizes over a narrow concentration range. The influences of bile salt concentration and species upon these micelles have relevance to the plasma transport of bile salts in high-density lipoproteins and to the physical-chemical state of apo A-I and apo A-II molecules in native biles.

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“…Given a torus with inner radius of 80-85 Å and outer radius of 100-105 Å, a cylinder with a radius of 1.00 nm was obtained with a length (L) of 10.1 nm and a volume of 10.1π nm 3 . We used σ cyl of 0.08 eq/nm 2 for the simulations [13].…”

mentioning

confidence: 99%

Adsorption of apolipoprotein A-I to biological membranes. A statistical mechanical model

Gross¹

2012

EPL

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Apolipoprotein A-I (apo A-I), the main protein component of high-density lipoprotein (HDL), reduces the risk for atherosclerosis by removing cholesterol from the membrane of foam cells. Experiments with model membrane systems have indicated, however, that membrane cholesterol reduces apo A-I binding to the membrane. Foam cells resolve this discrepancy electrostatically by co-inserting negatively charged phospholipids in their membrane. Here we present a statistical mechanical model to account for the effect of cholesterol. Our model is based on the Haugen and May model which takes into account the dipolar nature of the zwitterionic phospholipid head group in the membrane, in which the positive end of the zwitterionic dipole moment can move randomly on a hemispherical surface with a radius equal to the arm of the dipole moment and with the negative end fixed at the hydrocarbon layer. Adsorption of a positively charged apo A-I macroion to the surface of the membrane modifies the electric field within the head group region and induces lateral demixing of phospholipid molecules in the membrane. Results from numerical integration of model equations show that i) as a result of the strong charge-dipole electrostatic coupling, the positive end of the dipoles tilts away from the adsorbed macroion in a cooperative manner; and ii) cholesterol reduces macroion adsorption to the membrane by reducing the surface area of the membrane and restricting the dipoles range of rotation. Model predictions for the change in free energy of adsorption to zwitterionic membrane are in good agreement with previously reported experimental data with liposomes. The model can assist in designing new mimetic peptides.

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The surface charge of apolipoproteins, phospholipid liposomes, and human very low density lipoproteins.

Cited by 9 publications

References 50 publications

Stability, Hydration, and Thermodynamic Properties of RNase A Confined in Surface-Functionalized SBA-15 Mesoporous Molecular Sieves

Stability, Hydration, and Thermodynamic Properties of RNase A Confined in Surface-Functionalized SBA-15 Mesoporous Molecular Sieves

Self-association of human apolipoproteins A-I and A-II and interactions of apolipoprotein A-I with bile salts: quasi-elastic light scattering studies

Adsorption of apolipoprotein A-I to biological membranes. A statistical mechanical model

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