Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy

Jun Ando, Masanao Kinoshita, Jin Cui, Hiroyuki Yamakoshi, Kosuke Dodo, Katsumasa Fujita, Michio Murata, Mikiko Sodeoka

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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.

元の言語英語
ページ(範囲)4558-4563
ページ数6
ジャーナルProceedings of the National Academy of Sciences of the United States of America
112
発行部数15
DOI
出版物ステータス出版済み - 4 14 2015

All Science Journal Classification (ASJC) codes

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