title: Spatial and functional heterogeneity of sphingolipid-rich membrane domains.
abstract: Little is known about the organization of lipids in biomembranes. Lipid rafts are defined as sphingolipid- and cholesterol-rich clusters in the membrane. Details of the lipid distribution of lipid rafts are not well characterized mainly because of a lack of appropriate probes. Ganglioside GM1-specific protein, cholera toxin, has long been the only lipid probe of lipid rafts. Recently it was shown that earthworm toxin, lysenin, specifically recognizes sphingomyelin-rich membrane domains. Binding of lysenin to sphingomyelin is accompanied by the oligomerization of the toxin that leads to pore formation in the target membrane. In this study, we generated a truncated lysenin mutant that does not oligomerize and thus is non-toxic. Using this mutant lysenin, we showed that plasma membrane sphingomyelin-rich domains are spatially distinct from ganglioside GM1-rich membrane domains in Jurkat T cells. Like T cell receptor activation and cross-linking of GM1, cross-linking of sphingomyelin induced calcium influx and ERK phosphorylation in the cell. However, unlike CD3 or GM1, cross-linking of sphingomyelin did not induce significant protein tyrosine phosphorylation. Combination of lysenin and sphingomyelinase treatment suggested the involvement of G-protein-coupled receptor in sphingomyelin-mediated signal transduction. These results thus suggest that the sphingomyelin-rich domain provides a functional signal cascade platform that is distinct from those provided by T cell receptor or GM1. Our study therefore elucidates the spatial and functional heterogeneity of lipid rafts.
authors.affiliation: RIKEN, Wako, Saitama 351-0198, Japan. kiyokawa@biken.osaka-u.ac.jp
authors.forename: Etsuko
authors.initials: E
authors.lastname: Kiyokawa
authors.forename: Takeshi
authors.initials: T
authors.lastname: Baba
authors.forename: Naomi
authors.initials: N
authors.lastname: Otsuka
authors.forename: Asami
authors.initials: A
authors.lastname: Makino
authors.forename: Shinichi
authors.initials: S
authors.lastname: Ohno
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kobayashi
mesh_terms: D002460:Cell Line; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005677:G(M1) Ganglioside / Q000378:metabolism*; D006801:Humans; D016296:Mutagenesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics / Q000378:metabolism; D014118:Toxins, Biological
chemical_list: D011506:Proteins; D011994:Recombinant Proteins; D014118:Toxins, Biological; C107040:lysenin; D005677:G(M1) Ganglioside; D013108:Sphingomyelin Phosphodiesterase