Effect of de Novo Designed Peptides Interacting with the Lipid-Membrane Interface on the Stability of the Cubic Phases of the Monoolein Membrane

Abstract

Elucidation of the mechanism of transitions between the cubic phase and the liquid-crystalline (Lα) phase and between different cubic phases is essential for an understanding of the dynamics of biomembranes and the development of new crystallization techniques. Recently, we found that electrostatic interactions due to the surface charges of lipid membranes induce transitions between the cubic phase and Lα phase and between different cubic phases (Aota-Nakano, Y.; Li, S. J.; Yamazaki, M. Biochim. Biophys. Acta 1999, 1461, 96; Li, S. J.; Yamashita, Y.; Yamazaki, M. Biophys. J. 2001, 81, 983). In the present study, we used small-angle X-ray scattering to investigate the effects of a de novo designed peptide (WLFLLKKK, peptide-1, which has positive charges and a site that is partitioned in electrically neutral lipid-membrane interfaces) on the stability of the cubic phase of the monoolein (MO) membrane. As the peptide-1 concentration increased, a transition from the Q224 to the Q229 phase in the MO membrane at a 30 wt % lipid concentration occurred at R = 0.0090 (R is the molar ratio of peptide to MO), and at R ≥ 0.040, the MO/peptide-1 membranes were in the Lα phase. As the NaCl concentration in the bulk phase increased, for the MO/peptide-1 membranes in the Q229 phase in excess water, a Q229 phase to Q224 phase transition occurred at low concentrations of NaCl. Similarly, for the MO/peptide-1 membranes (R = 0.080) in excess water, at low NaCl concentrations, they were in the Lα phase, but at ≥0.40 M NaCl, they were in the Q224 phase. These results indicate that peptide-1 was partitioned in the membrane interface of the MO membrane, electrostatic interactions due to peptide-1 in the membrane interface make the Q229 phase more stable than the Q224 phase, and with larger electrostatic interactions, the Lα phase is more stable than these cubic phases. Increased peptide-1 concentration reduced the absolute value of spontaneous curvature of the MO/peptide-1 monolayer membrane. On the basis of these results, we discuss the mechanism of the effect of peptide-1 on the phase stability of the MO membranes.