Direct measurement of the energetics of association between myelin basic protein and phosphatidylserine vesicles

Ramsay, Glen D.; Prabhu, R. R.; Freire, Ernesto

doi:10.1021/bi00356a062

Cited by 32 publications

(29 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…5 B, open circles). This character resembles the effect of the myelin basic protein binding to PS liposomes reported previously (56). The initial exothermic phase shows the heat effect that is considerably larger than typical values observed for highaffinity ion binding to macromolecules (57) and is accompanied by a large entropy decrease (DS ¼ À580 cal/molK).…”

Section: Isothermal Titration Calorimetry Experimentssupporting

confidence: 80%

Gadolinium Ions Block Mechanosensitive Channels by Altering the Packing and Lateral Pressure of Anionic Lipids

Ermakov

Kamaraju

Sengupta

et al. 2010

Biophysical Journal

119

107

View full text Add to dashboard Cite

Effects of polyvalent ions on the lateral packing of phospholipids have been known for decades, but the physiological consequences have not been systematically studied. Gd(3+) is a relatively nonspecific agent that blocks mechano-gated channels with a variable affinity. In this study, we show that the large mechanosensitive channel MscL of Escherichia coli is effectively blocked by Gd(3+) only when reconstituted with negatively charged phospholipids (e.g., PS). Taking this lead, we studied effects of Gd(3+) on monolayers and unilamellar vesicles made of natural brain PS, DMPS, and its mixtures with DMPC. In monolayer experiments, we found that muM Gd(3+) present in the subphase leads to approximately 8% lateral compaction of brain PS (at 35 mN/m). Gd(3+) more strongly shrinks and rigidifies DMPS films causing a spontaneous liquid expanded-to-compact transition to the limiting 40 A(2)/mol. Pressure-area isotherms of uncharged DMPC were unaffected by Gd(3+), and neutralization of DMPS surface by low pH did not produce strong compaction. Upshifts of surface potential isotherms of DMPS monolayers reflected changes in the diffuse double layer due to neutralization of headgroup charges by Gd(3+), whereas the increased packing density produced up to a 200 mV change in the interfacial dipole potential. The slopes of surface potential versus reciprocal area predicted that Gd(3+) induced a modest ( approximately 18%) increase in the magnitude of the individual lipid dipoles in DMPS. Isothermal titration calorimetry indicated that binding of Gd(3+) to DMPS liposomes in the gel state is endothermic, whereas binding to liquid crystalline liposomes produces heat consistent with the isothermal liquid-to-gel phase transition induced by the ion. Both titration curves suggested a K(b) of approximately 10(6) M(-1). We conclude that anionic phospholipids serve as high-affinity receptors for Gd(3+) ions, and the ion-induced compaction generates a lateral pressure increase estimated as tens of mN/m. This pressure can "squeeze" the channel and shift the equilibrium toward the closed state.

show abstract

Section: Isothermal Titration Calorimetry Experimentssupporting

confidence: 80%

Gadolinium Ions Block Mechanosensitive Channels by Altering the Packing and Lateral Pressure of Anionic Lipids

Ermakov

Kamaraju

Sengupta

et al. 2010

Biophysical Journal

119

107

View full text Add to dashboard Cite

show abstract

“…and should produce an extended absorption or release of heat as reported previously (Ramsay et al, 1986;Myers et al, 1987). The apparent saturation of AH ( Figure 7C) would not be expected if aggregatiodfusion provided a significant heat component.…”

Section: -)supporting

confidence: 67%

“…However, enthalpy contributions due to vesicle aggregation (Ramsay et al, 1986) and fusion (Myers et al, 1987) were probably small. For example, each ITC peak was essentially complete within 1 min ( Figure 7B), similar to the time course for annexin VI.…”

Section: Relationship Between Ah and Intrinsic Fluorescencementioning

confidence: 98%

See 1 more Smart Citation

Direct Enthalpy Measurements of the Calcium-Dependent Interaction of Annexin V and VI with Phospholipid Vesicles

Plager¹,

Nelsestuen²

1994

Biochemistry

View full text Add to dashboard Cite

Annexins V and VI are two members of the annexin protein family, each of which associate with phospholipid vesicles in a calcium-dependent manner. They may be important intracellular calcium response elements. Titration calorimetry and spectroscopic techniques showed striking features of these interactions. For annexin V and VI, the total heat release from calcium-dependent binding to bilayer vesicles composed of phosphatidylserine/phosphatidylcholine was -25 and -38 kcal/mol, respectively. The enthalpy of association (delta Hassoc) for the respective protein-calcium interactions was about -11 and -5 kcal/mol. The delta Hassoc for the annexin VI-vesicle interaction was largely independent of the headgroup of the anionic phospholipid and of the pH from 7.1 to 8.4. Use of phosphatidylethanolamine as the neutral phospholipid resulted in a slightly more negative delta Hassoc. Enthalpy was either independent of vesicle size (annexin V) or showed a slightly more negative value for large vesicles (annexin VI). The delta Hassoc for annexin VI-membrane interaction was not constant during protein titration but became more exothermic with higher protein density on the membrane. This behavior was surprising because the equilibrium constant showed negative cooperativity with respect to protein density [Bazzi, M. D., & Nelsestuen, G. L. (1991) Biochemistry 30, 7970-7977]. Apparently, entropy changes occurred which were large and negative, thereby compensating for the increasingly negative enthalpy but decreasing affinity as protein density was increased. In fact, the exothermic process coincided more closely with a change in the intrinsic tryptophan fluorescence of annexin VI than with actual protein-membrane binding. Circular dichroism detected very small changes in protein secondary structure during these events. The observed delta Hassoc for annexin-membrane interaction appeared to involve contributions from the membrane as well as from the protein. Annexin-membrane binding may exert large effects on the membrane that could serve a regulatory capacity in the cell.

show abstract

“…The decrease in drug uptake throughout the titration can be explained by several simultaneous phenomena, such as saturation of the lipid membrane (Ramsay et al, 1986;Myers et al, 1987), electrostatic effects due to the binding of a charged molecule to the membrane (Lehrmann and Seelig, 1994), or even decrease of DH throughout the titration as a result of the change in the nature of the interaction (Ramsay et al, 1986).…”

Section: Calorimetric Titration Of Liposome Suspensions With Drug Solmentioning

confidence: 99%

Interaction of Antiinflammatory Drugs with EPC Liposomes: Calorimetric Study in a Broad Concentration Range

Matos

Lima

Reis

et al. 2004

Biophysical Journal

View full text Add to dashboard Cite

Isothermal titration calorimetry was used to characterize and quantify the partition of indomethacin and acemetacin between the bulk aqueous phase and the membrane of egg phosphatidylcholine vesicles. Significant electrostatic effects were observed due to binding of the charged drugs to the membrane, which implied the use of the Gouy-Chapman theory to calculate the interfacial concentrations. The binding/partition phenomenon was quantified in terms of the partition coefficient (K(p)), and/or the equilibrium constant (K(b)). Mathematical expressions were developed, either to encompass the electrostatic effects in the partition model, or to numerically relate partition coefficients and binding constants. Calorimetric titrations conducted under a lipid/drug ratio >100:1 lead to a constant heat release and were used to directly calculate the enthalpy of the process, DeltaH, and indirectly, DeltaG and DeltaS. As the lipid/drug ratio decreased, the constancy of reaction enthalpy was tested in the fitting process. Under low lipid/drug ratio conditions simple partition was no longer valid and the interaction phenomenon was interpreted in terms of binding isotherms. A mathematical expression was deduced for quantification of the binding constants and the number of lipid molecules associated with one drug molecule. The broad range of concentrations used stressed the biphasic nature of the interaction under study. As the lipid/drug ratio was varied, the results showed that the interaction of both drugs does not present a unique behavior in all studied regimes: the extent of the interaction, as well as the binding stoichiometry, is affected by the lipid/drug ratio. The change in these parameters reflects the biphasic behavior of the interaction-possibly the consequence of a modification of the membrane's physical properties as it becomes saturated with the drug.

show abstract

Direct measurement of the energetics of association between myelin basic protein and phosphatidylserine vesicles

Cited by 32 publications

References 19 publications

Gadolinium Ions Block Mechanosensitive Channels by Altering the Packing and Lateral Pressure of Anionic Lipids

Gadolinium Ions Block Mechanosensitive Channels by Altering the Packing and Lateral Pressure of Anionic Lipids

Direct Enthalpy Measurements of the Calcium-Dependent Interaction of Annexin V and VI with Phospholipid Vesicles

Interaction of Antiinflammatory Drugs with EPC Liposomes: Calorimetric Study in a Broad Concentration Range

Contact Info

Product

Resources

About