(380d) The Effect of Headgroup Charge on Symmetric and Asymmetric Phospholipid Bilayers

The presence of an electric transmembrane potential of around 100 mV in biological cells is due to a variety of factors, including the asymmetric distribution of charged phospholipids in each bilayer leaflet. Since charged phospholipids comprise a significant component of the overall phospholipid bilayer composition, understanding the effect of headgroup charge on membrane material properties has important implications in a variety of physiological processes, such as cellular signaling, endocytosis, and membrane protein function. Notably, the charge asymmetry of the cell membrane is altered during cancerous transformation. In this talk, we will discuss the impact of headgroup charge on the thickness, compressibility, and bending rigidity of artificial phospholipid membranes. We first create symmetric membranes with varying anionic DOPG and zwitterionic DOPC content which indicate that as the concentration of charged species increases, the membrane thickness and Young’s modulus concurrently increase. Next, we describe the development of an experimental platform to create planar, free-standing, phospholipid bilayers with independent control of the phospholipid composition on either leaflet. Voltage-dependent capacitance measurements reveal a transmembrane potential that scales with the degree of membrane charge asymmetry, ranging from 0 to 80 mV, however the membrane Young’s modulus is not merely a compositional weighting of the relative phospholipid components. Asymmetric membranes with the same overall phospholipid composition as their symmetric counterparts are thinner and less stiff, likely due to decreased headgroup electrostatic repulsion between leaflets. However, asymmetric bilayers with one leaflet composed of entirely zwitterionic phospholipids exhibit an increase in stiffness with increasing anionic lipid content in the opposing leaflet due to the development of a differential stress across the two leaflets. These results demonstrate quantitative biophysical insights into increasingly realistic artificial cell membrane mimics.