Effect of Positively Charged Short Peptides on Stability of Cubic Phases of Monoolein/Dioleoylphosphatidic Acid Mixtures

Abstract

To elucidate the stability and phase transition of cubic phases of biomembranes with infinite periodic minimal surface is indispensable from biological and physicochemical aspects. In this report, we investigated the effect of positively charged peptide-3K (LLKKK) and poly(L-lysine) on the phase stability of monoolein (MO) membranes containing negatively charged dioleoylphosphatidic acid (DOPA) (i.e., DOPA/MO membranes) using small-angle X-ray scattering. At first, the effect of peptide-3K on 10% DOPA/90% MO membrane in excess water, which is in the Q229 phase, was investigated. At 3.4 mM peptide-3K, a Q229 to Q230 phase transition occurred, and at >3.4 mM peptide-3K, the membrane was in the Q230 phase. Poly(L-lysine) (M(w) 1K-4K) also induced the Q230 phase, but peptide-2K (LLKK) could not induce it in the same membrane. We also investigated the effect of peptide-3K on the multilamellar vesicle (MLV) of 25% DOPA/75% MO membrane, which is in L(alpha) phase. In the absence of peptide, the spacing of MLV was very large (11.3 nm), but at > or = 8 mM peptide-3K, it greatly decreased to a constant value (5.2 nm), irrespective of the peptide concentration, indicating that peptide-3K and the membranes form an electrostatically stabilized aggregation with low water content. Poly(L-lysine) also decreased greatly the spacing of the 25% DOPA/75% MO MLV, indicating the formation of a similar aggregation. To compare the effects of peptide-3K and poly(L-lysine) with that of osmotic stress on stability of the cubic phase, we investigated the effect of poly(ethylene glycol) with molecular weight 7500 (PEG-6K) on the phase stability of 10% DOPA/90% MO membrane. With an increase in PEG-6K concentration, i.e., with an increase in osmotic stress, the most stable phase changed as follows; Q229 (Schwartz's P surface) --> Q224 (D) --> Q230 (G). On the basis of these results, we discuss the mechanism of the effects of the positively charged short peptides (peptide-3K) and poly(L-lysine) on the structure and phase stability of DOPA/MO membranes.

Tuning Curvature and Stability of Monoolein Bilayers by Designer Lipid-Like Peptide Surfactants

“…In a basic approach, the molecular shape can be described by the critical packing parameter (CPP) or the molecular wedge shape factor, which is defined as:where v s is the hydrophobic chain volume, a 0 is the headgroup area, and l is the hydrophobic chain length [73]. This packing parameter is controlled by various factors such as surfactant's molecular shape, temperature, hydration, the presence of hydrophilic or hydrophobic guest molecules, and electrostatic effects [16], [29]–[33], [35], [45]–[50], [61], [62].…”

“…Moreover, the effect of various peptides on the stability of MO-based cubic phases has been subject of several studies [61]–[64]. It was found that the electrostatic interactions in the membranes incorporating negatively (or positively) charged lipids are controlling the structural lamellar-nonlamellar transitions, i.e.…”

The Cubic “Faces” of Biomembranes

“…within the same cell organelle is frequently seen, pointing to the ease with which lamellar and bicontinuous cubic membranes or other organized membrane structures are interconverted. In vitro studies using monoolein membranes containing negatively charged dioleoylphosphatidic acid have shown that the electrostatic interactions caused by surface charge of the membranes [17], charged 2þ short peptides such as poly-L-lysine [18], Ca concentration [19], and low pH [20] play important role in the phase transition between lamellar and cubic phases as well as on the stability of cubic phases. Likewise, the weak molecular interactions, for example, by membrane proteins, may lead to transformation of Endoplasmic reticulum (ER) membrane from lamellar into cubic in mammalian cells suggesting that electrostatic interactions may play an important role in that process [18,21].…”

“…In vitro studies using monoolein membranes containing negatively charged dioleoylphosphatidic acid have shown that the electrostatic interactions caused by surface charge of the membranes [17], charged 2þ short peptides such as poly-L-lysine [18], Ca concentration [19], and low pH [20] play important role in the phase transition between lamellar and cubic phases as well as on the stability of cubic phases. Likewise, the weak molecular interactions, for example, by membrane proteins, may lead to transformation of Endoplasmic reticulum (ER) membrane from lamellar into cubic in mammalian cells suggesting that electrostatic interactions may play an important role in that process [18,21]. In a recent experimental study on the effects of divalent cations in the isolation buffers for mitochondria, we were able to demonstrate that the presence of high concentration of Ethylenediaminetetraacetic acid (EDTA) up to 10 mM preserved mitochondrial cubic membranes in vitro (manuscript in preparation).…”

The Single GUV Method for Probing Biomembrane Structure and Function

“…These have been postulated to play several important biological roles such as membrane fusion, control of functions of membrane proteins, and ultrastructural organization inside cells. One family of cubic phases, which includes the Q 224 phase (space group Pn3m, Schwartz's D surface), Q 229 phase (Im3m, P surface) and Q 230 phase (Ia3d, G surface), has an infinite periodic minimal surface (IPMS) consisting of bicontinu-ous regions of water and hydrocarbon [17][18][19]. We have found that, as the concentration of peptide-1 increased, a phase transition from Q 224 to Q 229 occurred, and that, at higher peptide-1 concentrations, MO/peptide-1 membranes were in the L α phase [16].…”