Synergistic effects of Ca²⁺ and wheat germ agglutinin on the lamellar‐hexagonal (H_II) phase transition of glycophorin‐containing egg‐phosphatidylethanolamine membranes

Abstract

Glycophorin has been reconstituted into egg phosphatidylethanolamine (egg-PtdEtn) membranes. Stable vesicles were obtained at a molar ratio of 8 x of inserted protein/lipid. This macroscopic change from lipid aggregates to lipid vesicles was followed by density gradient centrifugation. Vesicles formed in the presence of protein enclose the dye calcein and are stable with time and temperature. Membrane aggregation does not occur, as was demonstrated by energy-transfer experiments. The phase transition from the fluid lamellar L, phase to the inverted hexagonal HII phase observed at 29" C in pure egg-PtdEtn membranes is suppressed and finally disappears in the presence of glycophorin. The transition enthalpy decreases linearly from AH = 4 kJ/mol in pure lipids to zero at a protein/lipid molar ratio of 1 : 1000. Ca2 [8, 19 -211. A fluorimetric detection of the bilayer-to-hexagonal phase transition in diluted membrane suspension has been introduced which allows the analysis of the transition kinetics [22]. A recent review summarizes the actual knowledge of the structure of the inverted hexagonal (HII) phase and of the non-lamellar phase transitions of lipids [23].In addition to the application of different experimental techniques, models were developed postulating two types of inverted micellar structures [24]. Spherical inverted micelles (lipid particles) sandwiched between the lipid monolayers of a bilayer membrane are opposed to inverted micellar intermediates which are transient intermediates within an interbilayer attachment site necessary for the process of membrane aggregation, membrane fusion or the lamellar-to-hexagonal (HII) phase transition [25,26]. Siegel states that inverted micellar intermediates formed at the interface of interacting bilayers may either (a) revert or (b) transform into an interlamellar attachment or (c) into a HII-phase precursor formed via coalescence of inverted micellar intermediates in a pearl-string fashion. Beside this monolayer-encapsulated HII tube, which is called a rod micellar intermediate, Siegel proposes a second type of intermediate [25]. The coalescence of inverted micellar intermediates may also lead to the formation of line defects which than elongate into structures consisting of two opposed halves of HII tubes. Formations of interlamellar attachments, rod micellar intermediates, as well as line defects, ILA, RMI as well as LD depends on the density of inverted micellar intermediates within the bilayer membrane. The formation of HII precusors is accompanied by intramembraneous lipid mixing and in vesicle systems by leakage of aqueous content.

Structural and dynamical surface properties of phosphatidylethanolamine containing membranes

“…According to previous results, EggPE gel-L α transition is, at pH 7.0, at 10-11 °C and the L α -H II transition at 28-31 °C, as measured by differential scanning calorimetry and ESR [38,39]. In addition, the gel-L α transition in DMPE is around 50 °C [40][41][42].…”

Life‐threatening hemolytic anemia due to an autoanti‐Pr cold agglutinin: evidence that glycophorin A antibodies may induce lipid bilayer exposure and cation permeability independent of agglutination

“…Our results suggest a novel mechanism where antibodies to GPA can damage a subpopulation of RBCs by increased exposure of PE and membrane permeability and the transient formation of cation-permeable lipid pores. 46 The magnitude of the clinical (in vivo) hemolysis suggests that physical stress on RBCs in the circulation is an important factor.…”

Self-assembly of large, ordered lamellae from non-bilayer lipids and integral membrane proteinsin vitro

“…3) or stabilize the lamellar phase in the presence of high concentrations of non-bilayer lipids (28). In general, lipid polymorphism can be modulated by different membrane components and environmental factors (2,29).…”