Membrane properties of ether-type phosphatidylcholine bearing partially fluorinated C18-monoacetylenic chains and their applicability to membrane protein reconstitution matrices

Abstract

To examine the applicability of fluorinated membrane-forming phospholipids to reconstitution matrices for functional membrane proteins, the membrane properties of a synthetic ether-type phosphatidylcholine (PC) bearing partially fluorinated C18-monoacetylenic (9-octadecynyl) chains, DF8CCH8PC, were compared with those of its non-fluorinated counterpart, DH8CCH8PC. Light-harvesting complex 2 (LH2) and the light-harvesting 1‒reaction center core complex (LH1-RC) isolated from purple photosynthetic bacteria were employed as probe membrane proteins to evaluate the extent to which their reconstitution into DF8CCH8PC membranes could proceed. DF8CCH8PC formed more expanded and more stable fluid monolayers than DH8CCH8PC at the air-water interface at 25 °C; the former PC molecule occupied an area of ca. 0.70 nm2 at a collapse pressure, πc, of 52 mN/m, while the latter occupied an area of ca. 0.55 nm2 at a πc of 45 mN/m. In contrast, the molecular motion detected using fluorescent probes was much more restricted in DF8CCH8PC bilayers than in DH8CCH8PC ones. Although the reconstitution efficiencies of both LH2 and LH1-RC into DF8CCH8PC bilayers were lower than those into DH8CCH8PC bilayers, the membrane proteins incorporated into DF8CCH8PC bilayers showed increased thermostability. The increased thermostability of these proteins in fluorinated PC membranes might be due to the restricted molecular motion in the hydrophobic chains. The results of this study suggest that partially fluorinated PCs can be useful materials for the construction of lipid‒functional membrane protein assemblies including large membrane protein complexes, such as LH1-RC, for biotechnological applications.