Effect of Hybrid Lipid on Line Tension and Universality in Lipid Membranes

Abstract

Giant unilamellar vesicles (GUVs) can be used for direct investigation of many phenomena. When they are made of at least three components, one being cholesterol, one a high-melting-point lipid and one a low-melting-point lipid, GUVs can exhibit coexisting liquid ordered -liquid disordered phases resulting in micron-sized membrane domains. The energy per unit length of boundary is called line tension, which affects the sizes and shapes of the domains. Line tension depends on the temperature of the system according to power law and vanishes at critical temperature. Universal scaling behavior can help us to understand the phase behavior of many different systems. Systems in the same universality class represent similar collective behavior in phase transitions apart although they have different physical features. Critical exponents characterize the continuous phase transition of systems, and all systems belonging to a universality class will have the same critical exponents. In this work, we measured the critical exponent related to line tension using fluorescence microscopy and image processing. We investigated the effects of hybrid lipid on line tension and critical exponent. Hybrid lipids are abundant in cell membranes. One chain of hybrid lipid is saturated and the other one is unsaturated, because of which they behave as linactants and can reduce the line tension. We prepared GUVs with three different compositions: DOPC/DSPC/Cholesterol 30:45:25, DOPC/DSPC/POPC/Cholesterol 22.5:45:25:7.5, DOPC/DSPC/POPC/Cholesterol 15:45:55:25. The first system does not contain hybrid lipid; but in second and third systems, 25% and 50% of unsaturated lipid (DOPC) were replaced with hybrid lipid (POPC), respectively. Our results show that the critical exponent associated with line tension gradually increase with hybrid lipid concentration. Having different values of critical exponent in different mixtures indicate that lipid bilayers cannot be classified in a universality class. Correction et al.Biophysical JournalApril 16, 2013In Brief2013. Effect of Hybrid Lipid on Line Tension and Universality in Lipid Membranes. Eda Baykal-Caglar, Juyang Huang. Biophys. J. 104(2)s: 589a. Full-Text PDF Open Archive