Quantifying growth of symmetric and asymmetric lipid bilayer domains

Here, we examine by atomic force microscopy (AFM) the kinetics and morphology of lipid domain growth during lipid phase separation by rapid thermal cooling of fully mixed two-component supported lipid bilayers. At the undercooled temperatures chosen, symmetric 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-rich domains favored slower reaction-limited growth whereas asymmetric galactosylceramide (GalCer)-rich domains favored faster diffusion-limited growth, indicated by shape factors and kinetic exponents. Because kinetically limited conditions could be accessed, we were able to estimate the activation energy barrier (approximately 16kT) and lateral diffusion coefficient (approximately 0.20 microm2/s) of lipid molecular addition to a growing domain. We discuss these results with respect to transition states, obstructed diffusion, and the necessity for coordinating growth in both leaflets in a symmetric lipid domain.