Membrane partitioning of the pore-forming domain of colicin A. Role of the hydrophobic helical hairpin.

The colicins are bacteriocins that target Escherichia coli and kill bacterial cells through different mechanisms. Colicin A forms ion channels in the inner membranes of nonimmune bacteria. This activity resides exclusively in its C-terminal fragment (residues 387-592).

The onset of Triton X-100 solubilization of sphingomyelin/ceramide bilayers: effects of temperature and composition.

The early stages of Triton X-100 solubilization of bilayers consisting of sphingomyelin/ceramide (SM/Cer) mixtures have been studied using a combination of calorimetric and spectroscopic techniques. Compositions based on sphingomyelin, containing up to 30 mol% Cer, at 4, 20 and 50°C have been examined. The presence of Cer does not modify the affinity (in terms of ΔG of binding per mol total lipid) of the SM-based bilayers for Triton X-100, although it does increase the amount of detergent required for the onset of solubilization.

Triton X-100 partitioning into sphingomyelin bilayers at subsolubilizing detergent concentrations: effect of lipid phase and a comparison with dipalmitoylphosphatidylcholine.

We examined the partitioning of the nonionic detergent Triton X-100 at subsolubilizing concentrations into bilayers of either egg sphingomyelin (SM), palmitoyl SM, or dipalmitoylphosphatidylcholine. SM is known to require less detergent than phosphatidylcholine to achieve the same extent of solubilization, and for all three phospholipids solubilization is temperature dependent. In addition, the three lipids exhibit a gel-fluid phase transition in the 38-41 degrees C temperature range.

Interaction of human apolipoprotein A-I with model membranes exhibiting lipid domains.

Several mechanisms for cell cholesterol efflux have been proposed, including membrane microsolubilization, suggesting that the existence of specific domains could enhance the transfer of lipids to apolipoproteins. In this work isothermal titration calorimetry, circular dichroism spectroscopy, and two-photon microscopy are used to study the interaction of lipid-free apolipoprotein A-I (apoA-I) with small unilamellar vesicles (SUVs) of 1-palmitoyl, 2-oleoyl phosphatidylcholine (POPC) and sphingomyelin (SM), with and without cholesterol. Below 30 degrees C the calorimetric results show that apoA-I interaction with POPC/SM SUVs produces an exothermic reaction, characterized as nonclassical hydrophobic binding.

Enthalpy-driven apolipoprotein A-I and lipid bilayer interaction indicating protein penetration upon lipid binding.

The interaction of lipid-free apolipoprotein A-I (apoA-I) with small unilamellar vesicles (SUVs) of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) with and without free cholesterol (FC) was studied by isothermal titration calorimetry and circular dichroism spectroscopy. Parameters reported are the affinity constant (K(a)), the number of protein molecules bound per vesicle (n), enthalpy change (DeltaH degrees), entropy change (DeltaS degrees ), and the heat capacity change (DeltaC(p) degrees). The binding process of apoA-I to SUVs of POPC plus 0-20% (mole) FC was exothermic between 15 and 37 degrees C studied, accompanied by a small negative entropy change, making enthalpy the main driving force of the interaction.

Interaction of apolipoprotein A-I in three different conformations with palmitoyl oleoyl phosphatidylcholine vesicles.

Interactions of apolipoprotein A-I (apoA-I) with cell membranes appear to be important in the initial steps of reverse cholesterol transport. The objective of this work was to examine the effect of three distinct conformations of apoA-I (lipid-free and in 78 A or 96 A reconstituted high density lipoproteins, rHDL) on its ability to bind to, and abstract lipids from, palmitoyl oleoyl phosphatidylcholine membrane vesicles (small unilamellar vesicles, SUV, and giant unilamellar vesicles, GUV). The molecular interactions were observed by two-photon fluorescence microscopy, and the binding parameters were quantified by gel-permeation chromatography or isothermal titration microcalorimetry.