title: Lipid bilayers containing sphingomyelins and ceramides of varying N-acyl lengths: a glimpse into sphingolipid complexity.
abstract: The thermotropic properties of aqueous dispersions of sphingomyelins (SM) and ceramides (Cer) with N-acyl chains varying from C6:0 to C24:1, either pure or in binary mixtures, have been examined by differential scanning calorimetry. Even in the pure state, Cer and particularly SM exhibited complex endotherms, and their thermal properties did not vary in a predictable way with changes in structure. In some cases, e.g. C18:0 SM, atomic force microscopy revealed coexisting lamellar domains made of a single lipid. Partial chain interdigitation and metastable crystalline states were deemed responsible for the complex behavior. SM:Cer mixtures (90:10mol ratio) gave rise to bilayers containing separate SM-rich and Cer-rich domains. In vesicles made of more complex mixtures (SM:PE:Chol, 2:1:1), it is known that sphingomyelinase degradation of SM to Cer is accompanied by vesicle aggregation and release of aqueous contents. These vesicles did not reveal observable domain separation by confocal microscopy. Vesicle aggregation occurred at a faster rate for those bilayers that appeared to be more fluid according to differential scanning calorimetry. Content efflux rates measured by fluorescence spectroscopy were highest with C18:0 and C18:1 SM, and in general those rates did not vary regularly with other physical properties of SM or Cer. In general the individual SM and Cer appear to have particular thermotropic properties, often unrelated to the changes in N-acyl chain.
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Noemi
authors.initials: N
authors.lastname: Jiménez-Rojo
authors.forename: Aritz B
authors.initials: AB
authors.lastname: García-Arribas
authors.forename: Jesús
authors.initials: J
authors.lastname: Sot
authors.forename: Alicia
authors.initials: A
authors.lastname: Alonso
authors.forename: Félix M
authors.initials: FM
authors.lastname: Goñi
mesh_terms: D001409:Bacillus cereus / Q000737:chemistry / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry; D002518:Ceramides / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D013108:Sphingomyelin Phosphodiesterase / Q000737:chemistry; D013109:Sphingomyelins / Q000737:chemistry*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D002518:Ceramides; D008051:Lipid Bilayers; D013109:Sphingomyelins; D002784:Cholesterol; D013108:Sphingomyelin Phosphodiesterase
keywords: Atomic force microscopy; Ceramide; Differential scanning calorimetry; Interdigitation; Sphingomyelin; Sphingomyelinase