On the Propensity of Phosphatidylglycerols to Form Interdigitated Phases

We have determined the phase behavior of disaturated phosphatidylglycerols (PGs) of chain lengths nCH2=14–18 at high pH and ionic strength using calorimetry, dilatometry, as well as x-ray diffraction. PGs with nCH2=14 and 16 show thermotropic behavior similar to that of phosphatidylcholines (PCs). T...

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Bibliographic Details
Published in:Biophysical journal 2007-07, Vol.93 (2), p.513-525
Main Authors: Pabst, Georg, Danner, Sabine, Karmakar, Sanat, Deutsch, Günter, Raghunathan, Velayudhan A.
Format: Article
Language:English
Subjects:
Balancing
Biochemistry
Biophysical Phenomena
Biophysics
Calorimetry, Differential Scanning
Chains
Chemical bonds
Diffraction
Dilatometry
Gels
Hydrogen-Ion Concentration
Lipids
Membranes
Osmolar Concentration
Peptides
Phases
Phosphatidylglycerols - chemistry
Scattering, Small Angle
Thermodynamics
Tilt
X-Ray Diffraction
X-rays
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Summary:We have determined the phase behavior of disaturated phosphatidylglycerols (PGs) of chain lengths nCH2=14–18 at high pH and ionic strength using calorimetry, dilatometry, as well as x-ray diffraction. PGs with nCH2=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.
ISSN:0006-3495
1542-0086
DOI:10.1529/biophysj.106.101592