Cholesterol displaces palmitoylceramide from its tight packing with palmitoylsphingomyelin in the absence of a liquid-disordered phase.
A set of different biophysical approaches has been used to explore the phase behavior of palmitoylsphingomyelin (pSM)/cholesterol (Chol) model membranes in the presence and absence of palmitoylceramide (pCer). Fluorescence spectroscopy of di-4-ANEPPDHQ-stained pSM/Chol vesicles and atomic force microscopy of supported planar bilayers show gel L(beta)/liquid-ordered (L(o)) phase coexistence within the range X(Chol) = 0-0.25 at 22 degrees C. At the latter compositional point and beyond, a single L(o) pSM/Chol phase is detected. In ternary pSM/Chol/pCer mixtures, differential scanning calorimetry of multilamellar vesicles and confocal fluorescence microscopy of giant unilamellar vesicles concur in showing immiscibility, but no displacement, between L(o) cholesterol-enriched (pSM/Chol) and gel-like ceramide-enriched (pSM/pCer) phases at high pSM/(Chol + pCer) ratios. At higher cholesterol content, pCer is unable to displace cholesterol at any extent, even at X(Chol) < 0.25. It is interesting that an opposite strong cholesterol-mediated pCer displacement from its tight packing with pSM is clearly detected, completely abolishing the pCer ability to generate large microdomains and giving rise instead to a single ternary phase. These observations in model membranes in the absence of the lipids commonly used to form a liquid-disordered phase support the role of cholesterol as the key determinant in controlling its own displacement from L(o) domains by ceramide upon sphingomyelinase activity.
Busto
Jon V
JV
Unidad de Biofísica (Centro Mixto CSIC-UPV/EHU), and Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain.
Sot
Jesús
J
Requejo-Isidro
José
J
Goñi
Félix M
FM
Alonso
Alicia
A
D002518:Ceramides / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D044367:Phase Transition; D011726:Pyridinium Compounds / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013109:Sphingomyelins / Q000737:chemistry*; D013696:Temperature
D002518:Ceramides; D011726:Pyridinium Compounds; D013109:Sphingomyelins; C541550:di-4-ANEPPDHQ; C033171:palmitoylsphingomyelin; C097760:N-palmitoylsphingosine; D002784:Cholesterol