title: On the propensity of phosphatidylglycerols to form interdigitated phases.
abstract: We have determined the phase behavior of disaturated phosphatidylglycerols (PGs) of chain lengths n(CH2) = 14-18 at high pH and ionic strength using calorimetry, dilatometry, as well as x-ray diffraction. PGs with n(CH2) = 14 and 16 show thermotropic behavior similar to that of phosphatidylcholines (PCs). The area/lipid obtained in the gel phase is smaller than that reported for PCs despite the expected larger effective headgroup size. This can be explained by the tilting of the PG headgroup out of the bilayer plane, and we provide experimental evidence for a headgroup tilt transition. For distearoyl PG, we further find that the "usual" gel phase coexists with an interdigitated phase, which exhibits a transition from an orthorhombic into a hexagonal chain packing. The total amount of the interdigitated phase depends significantly on the temperature but is found to be largely independent of temperature equilibration time and different sample preparation protocols. Thus, the development of the interdigitated phase appears to be kinetically trapped. The formation of interdigitated phases in PGs at much smaller chain lengths than in PCs is of high relevance to interaction studies with antimicrobial peptides, as it provides a mechanism for the discrimination of membranes composed of different lipid species.
authors: Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, 8042 Graz, Austria. Georg.Pabst@oeaw.ac.at
authors: Georg
authors: G
authors: Pabst
authors: Sabine
authors: S
authors: Danner
authors: Sanat
authors: S
authors: Karmakar
authors: Günter
authors: G
authors: Deutsch
authors: Velayudhan A
authors: VA
authors: Raghunathan
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002152:Calorimetry, Differential Scanning; D005782:Gels; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D010715:Phosphatidylglycerols / Q000737:chemistry*; D053838:Scattering, Small Angle; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D005782:Gels; D010715:Phosphatidylglycerols; C084352:distearoyl phosphatidylglycerol; C002773:dimyristoylphosphatidylglycerol; C030345:1,2-dipalmitoylphosphatidylglycerol