Coexistence of two liquid crystalline phases in dihydrosphingomyelin and dioleoylphosphatidylcholine binary mixtures |
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Authors: | Masanao Kinoshita Nobuaki Matsumori Michio Murata |
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Institution: | 1. JST ERATO, Lipid Active Structure Project, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan;2. Project Research Center for Fundamental Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan;3. Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan |
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Abstract: | Recently, DHSM, a minor constituent in naturally occurring SMs, was indicated to form a raft-like ordered phase more effectively than a naturally occurring form of SM because DHSM has greater potential to induce the intermolecular hydrogen bond. In order to examine the influence of the DHSM-induced hydrogen bond on the phase segregation, the thermal phase behavior of stearoyl-DHSM/DOPC binary bilayers was examined using calorimetry and fluorescence observation and compared with that of SSM/DOPC binary bilayers. Results revealed that the DHSM/DOPC bilayers undergo phase segregation between two Lα phases within a limited compositional range. On the other hand, apparent phase separation was not observed above main transition temperature in SSM/DOPC mixtures. Our monolayer measurements showed that the lipid packing of DHSM is less perturbed than that of SSM by the addition of small amount of DOPC, indicating a stronger hydrogen bond between DHSM molecules. Therefore, in DHSM/DOPC binary bilayers, DHSM molecules may locally accumulate to form a DHSM-rich domain due to a DHSM-induced hydrogen bond. On the other hand, excess accumulation of DHSM should be prevented because the difference in the curvature between DHSM and DOPC assemblies causes elastic constraint at the domain boundary between the DHSM-rich and DOPC-rich domains. Competition between the energetic advantages provided by formation of the hydrogen bond and the energetic disadvantage conferred by elastic constraints likely results in Lα/Lα phase separation within a limited compositional range. |
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Keywords: | DHSM dihydrosphingomyelin SM sphingomyelin DOPC 1 2-dioleoyl-sn-phosphatidylcholine SSM stearoyl-SM Lα phase fluid phase chol cholesterol DSC differential scanning calorimetry SAXD small angle x-ray diffraction Lβ phase gel phase FCS fluorescent correlation spectroscopy Pβ phase ripple phase Lo phase liquid ordered phase Ld phase liquid disordered phase GUV giant unilamellar vesicle NMR nuclear magnetic resonance PE phosphatidylethanolamine bodipy-PC 2-(4 4-difluoro-5 7-dimethyl-4-bora-3a 4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glyceo-3-phosphocholine Lc phase subgel phase TR-DPPE Texas-red dipalmitoylphosphatidylethanolamine DEPC 1 2-dielaidoyl-sn-phosphatidylcholine DPPE 1 2-dipalmitoyl-sn-phosphatidylethanolamine |
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