Apolipophorin III interaction with model membranes composed of phosphatidylcholine and sphingomyelin using differential scanning calorimetry

Abstract

Apolipophorin III (apoLp-III) from Locusta migratoria was employed as a model apolipoprotein to gain insight into binding interactions with lipid vesicles. Differential scanning calorimetry (DSC) was used to measure the binding interaction of apoLp-III with liposomes composed of mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and sphingomyelin (SM). Association of apoLp-III with multilamellar liposomes occurred over a temperature range around the liquid crystalline phase transition (Lα). Qualitative and quantitative data were obtained from changes in the lipid phase transition upon addition of apoLp-III. Eleven ratios of DMPC and SM were tested from pure DMPC to pure SM. Broadness of the phase transition (T1/2), melting temperature of the phase transition (Tm) and enthalpy were used to determine the relative binding affinity to the liposomes. Multilamellar vesicles composed of 40% DMPC and 60% SM showed the greatest interaction with apoLp-III, indicated by large T1/2 values. Pure DMPC showed the weakest interaction and liposomes with lower percentage of DMPC retained domains of pure DMPC, even upon apoLp-III binding indicating demixing of liposome lipids. Addition of apoLp-III to rehydrated liposomes was compared to codissolved trials, in which lipids were rehydrated in the presence of protein, forcing the protein to interact with the lipid system. Similar trends between the codissolved and non-codissolved trials were observed, indicating a similar binding affinity except for pure DMPC. These results suggested that surface defects due to non-ideal packing that occur at the phase transition temperature of the lipid mixtures are responsible for apolipoprotein-lipid interaction in DMPC/SM liposomes.

Apolipoprotein-induced conversion of phosphatidylcholine bilayer vesicles into nanodisks

“…Since an increase in DG content in insect lipoproteins is the trigger for apoLp-III binding in vivo, it was tested if DG was able to enhance DMPC solubility rates similar to cholesterol. In addition, SM was used as this is a major HDL lipid component and increased binding was observed in DMPC/SM LUV mixtures (40:60% mol) using differential scanning calorimetric analysis [25]. Surprisingly, addition of neither DG nor SM did result in increased solubility rates.…”

Differential scanning calorimetry: An invaluable tool for a detailed thermodynamic characterization of macromolecules and their interactions

“…[4950] Studies on the lipid interaction of cytochrome C oxidase showed that one oxidase molecule perturbed over 70 lipid molecules corresponding to the lipids surrounding the protein. [51] For a review on membrane proteins and DSC refer to.…”

“…Protein-lipid interactions such as the interaction of various apoproteins with different lipid mixtures have been investigated showing preferential binding to specific matrices. [ 49 50 ] Studies on the lipid interaction of cytochrome C oxidase showed that one oxidase molecule perturbed over 70 lipid molecules corresponding to the lipids surrounding the protein. [ 51 ] For a review on membrane proteins and DSC refer to.…”