Cholesterol-Induced Interfacial Area Condensations of Galactosylceramides and Sphingomyelins with Identical Acyl Chains
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- 作者：Janice M. Smaby ; Maureen Momsen ; Vitthal S. Kulkarni ; and Rhoderick E. Brown
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：May 7, 1996
- 年：1996
- 卷：35
- 期：18
- 页码：5696 - 5704
- 全文大小：338K
- 年卷期：v.35,no.18(May 7, 1996)
- ISSN：1520-4995
文摘
The interfacial interactions occurring between cholesterol andeither galactosylceramides(GalCers) or sphingomyelins (SMs) with identical acyl chains have beeninvestigated using Langmuirfilm balance techniques. Included among the synthesized GalCersand SMs were species containingpalmitoyl (16:0), stearoyl (18:0), oleoyl[18:1
9(c)], nervonoyl[24:115(c)], or linoleoyl[18:29,12(c)] acylresidues. The cholesterol-induced condensations in the averagemolecular areas of the monolayers weredetermined by classic mean molecular area vs composition plots as wellas by expressing the changes interms of sphingolipid cross-sectional area reduction over the surfacepressure range from 1 to 40 mN/m(at 1 mN/m intervals). The results show that, at surface pressuresapproximating bilayer conditions (30mN/m), acyl heterogeneity in naturally occurring SMs (bovine or egg SM)enhanced the area condensationinduced by cholesterol compared to their predominant molecular species(e.g. 18:0 SM in bovine SM;16:0 SM in egg SM). Nonetheless, cholesterol always had a greatercondensing effect on SM comparedto GalCer when these sphingolipids were acyl chain matched and insimilar phase states (prior to mixingwith cholesterol). Also, the cholesterol-induced area changes fora given sphingolipid type (e.g. SM orGalCer) were similar whether the acyl chains were saturated,cis-9-monounsaturated, orcis-9,12-diunsaturated if the sphingolipids were in similar phase states (priorto mixing with cholesterol) andcompared at equivalent surface pressures. These results indicatethat, under conditions where hydrocarbonstructure is matched, the sphingolipid head group plays a dominant rolein determining the extent towhich cholesterol reduces sphingolipid cross-sectional area.Despite the larger cholesterol-induced areacondensations observed in SMs compared to those in GalCers, themolecular-packing densities showedthat equimolar GalCer-cholesterol films were generally packed astight as or slightly tighter than thoseof the SM-cholesterol films. The results are discussed in termsof a molecular model for sphingolipid-cholesterol interactions. Our findings also not only raisequestions as to whether cholesterol-inducedcondensation data provide a reliable measure of the affinity, i.e.interaction strength, between cholesteroland different lipids but also provide insight regarding the stabilityof sterol/sphingolipid-rich microdomainsthought to exist in caveolae and other cell membraneregions.
9(c)], nervonoyl[24:115(c)], or linoleoyl[18:29,12(c)] acylresidues. The cholesterol-induced condensations in the averagemolecular areas of the monolayers weredetermined by classic mean molecular area vs composition plots as wellas by expressing the changes interms of sphingolipid cross-sectional area reduction over the surfacepressure range from 1 to 40 mN/m(at 1 mN/m intervals). The results show that, at surface pressuresapproximating bilayer conditions (30mN/m), acyl heterogeneity in naturally occurring SMs (bovine or egg SM)enhanced the area condensationinduced by cholesterol compared to their predominant molecular species(e.g. 18:0 SM in bovine SM;16:0 SM in egg SM). Nonetheless, cholesterol always had a greatercondensing effect on SM comparedto GalCer when these sphingolipids were acyl chain matched and insimilar phase states (prior to mixingwith cholesterol). Also, the cholesterol-induced area changes fora given sphingolipid type (e.g. SM orGalCer) were similar whether the acyl chains were saturated,cis-9-monounsaturated, orcis-9,12-diunsaturated if the sphingolipids were in similar phase states (priorto mixing with cholesterol) andcompared at equivalent surface pressures. These results indicatethat, under conditions where hydrocarbonstructure is matched, the sphingolipid head group plays a dominant rolein determining the extent towhich cholesterol reduces sphingolipid cross-sectional area.Despite the larger cholesterol-induced areacondensations observed in SMs compared to those in GalCers, themolecular-packing densities showedthat equimolar GalCer-cholesterol films were generally packed astight as or slightly tighter than thoseof the SM-cholesterol films. The results are discussed in termsof a molecular model for sphingolipid-cholesterol interactions. Our findings also not only raisequestions as to whether cholesterol-inducedcondensation data provide a reliable measure of the affinity, i.e.interaction strength, between cholesteroland different lipids but also provide insight regarding the stabilityof sterol/sphingolipid-rich microdomainsthought to exist in caveolae and other cell membraneregions.