Experimental and computational insight into the surface curvature of DPPS lipid bilayers

Understanding the structure and function of inherently asymmetric eukaryotic plasma membranes is almost inevitably preceded by the research into the structural and dynamic features of single- lipid symmetric membranes [1]. Among the latter, the most common lipid membranes are those built from zwitterionic phosphatidylcholine (PC) lipids present in both membrane leaflets, while those made from the major anionic phosphatidylserine (PS) lipid dominantly found in the inner membrane leaflet are significantly less common [2]. Apart from studies focusing on multilamellar liposomes (MLV) made from 1, 2-dipalmitoyl-sn-glycero- 3phospho-L-serine (DPPS) [3], the studies of corresponding unilamellar liposomes (LUV) are extremely rare. With the aim of shedding the light on the structure and properties of LUVs made of DPPS lipids, we present calorimetric, spectroscopic and MD simulation study of DPPS in the form of LUV in a phosphate buffer (pH = 7.4), with the corresponding MLV examined as a reference. Melting of LUV in a wide temperature range (50-59 °C), associated with rather high uncertainty data level emerged from temperature- dependent UV/Vis spectra (Fig. 1) is presumably related with LUV instability and/or fluctuation of structural features on LUV surface. The signatures of carbonyl backbone obtained from FTIR data support the existence of highly curved surface of LUV, the phenomenon of which is not observed in MLV, whereas MD data unravel the contribution of interlamellar water on the surface features in MLV.