title: Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy.
abstract: Sphingomyelin (SM) and cholesterol (chol)-rich domains in cell membranes, called lipid rafts, are thought to have important biological functions related to membrane signaling and protein trafficking. To visualize the distribution of SM in lipid rafts by means of Raman microscopy, we designed and synthesized an SM analog tagged with a Raman-active diyne moiety (diyne-SM). Diyne-SM showed a strong peak in a Raman silent region that is free of interference from intrinsic vibrational modes of lipids and did not appear to alter the properties of SM-containing monolayers. Therefore, we used Raman microscopy to directly visualize the distribution of diyne-SM in raft-mimicking domains formed in SM/dioleoylphosphatidylcholine/chol ternary monolayers. Raman images visualized a heterogeneous distribution of diyne-SM, which showed marked variation, even within a single ordered domain. Specifically, diyne-SM was enriched in the central area of raft domains compared with the peripheral area. These results seem incompatible with the generally accepted raft model, in which the raft and nonraft phases show a clear biphasic separation. One of the possible reasons is that gradual changes of SM concentration occur between SM-rich and -poor regions to minimize hydrophobic mismatch. We believe that our technique of hyperspectral Raman imaging of a single lipid monolayer opens the door to quantitative analysis of lipid membranes by providing both chemical information and spatial distribution with high (diffraction-limited) spatial resolution.
authors.affiliation: Sodeoka Live Cell Chemistry Project, Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology, Saitama 351-0198, Japan; Core Research for Evolutionary Science and Technology (CREST), JST, Saitama 351-0198, Japan; Department of Applied Physics, Osaka University, Osaka 565-0871, Japan; Synthetic Organic Chemistry Laboratory, RIKEN, Saitama 351-0198, Japan; and.
authors.forename: Jun
authors.initials: J
authors.lastname: Ando
authors.affiliation: Lipid Active Structure Project, JST, Exploratory Research for Advanced Technology, Project Research Center for Fundamental Science, and.
authors.forename: Masanao
authors.initials: M
authors.lastname: Kinoshita
authors.affiliation: Lipid Active Structure Project, JST, Exploratory Research for Advanced Technology, Department of Chemistry, Graduate School of Science, Osaka University, Osaka 560-0043, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Cui
authors.affiliation: Sodeoka Live Cell Chemistry Project, Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology, Saitama 351-0198, Japan; Synthetic Organic Chemistry Laboratory, RIKEN, Saitama 351-0198, Japan; and.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamakoshi
authors.affiliation: Sodeoka Live Cell Chemistry Project, Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology, Saitama 351-0198, Japan; Core Research for Evolutionary Science and Technology (CREST), JST, Saitama 351-0198, Japan; Synthetic Organic Chemistry Laboratory, RIKEN, Saitama 351-0198, Japan; and.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Dodo
authors.affiliation: Sodeoka Live Cell Chemistry Project, Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology, Saitama 351-0198, Japan; Core Research for Evolutionary Science and Technology (CREST), JST, Saitama 351-0198, Japan; Department of Applied Physics, Osaka University, Osaka 565-0871, Japan;
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Fujita
authors.affiliation: Lipid Active Structure Project, JST, Exploratory Research for Advanced Technology, Department of Chemistry, Graduate School of Science, Osaka University, Osaka 560-0043, Japan murata@chem.sci.osaka-u.ac.jp sodeoka@riken.jp.
authors.forename: Michio
authors.initials: M
authors.lastname: Murata
authors.affiliation: Sodeoka Live Cell Chemistry Project, Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology, Saitama 351-0198, Japan; Core Research for Evolutionary Science and Technology (CREST), JST, Saitama 351-0198, Japan; Synthetic Organic Chemistry Laboratory, RIKEN, Saitama 351-0198, Japan; and murata@chem.sci.osaka-u.ac.jp sodeoka@riken.jp.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Sodeoka
mesh_terms: D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D008567:Membranes, Artificial; D018613:Microscopy, Confocal / Q000379:methods*; D015394:Molecular Structure; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D015203:Reproducibility of Results; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013109:Sphingomyelins / Q000737:chemistry / Q000378:metabolism*; D053835:Unilamellar Liposomes / Q000378:metabolism
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D053835:Unilamellar Liposomes; D002784:Cholesterol; C017251:1,2-oleoylphosphatidylcholine
keywords: Raman imaging; alkyne tag; lipid raft; sphingomyelin; supported monolayer
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