CERT mediates intermembrane transfer of various molecular species of ceramides.
Ceramide produced at the endoplasmic reticulum is transported to the Golgi apparatus for conversion to sphingomyelin. The main pathway of endoplasmic reticulum-to-Golgi transport of ceramide is mediated by CERT, a cytosolic 68-kDa protein, in a nonvesicular manner. CERT contains a domain that catalyzes the intermembrane transfer of natural C(16)-ceramide. In this study, we examined the ligand specificity of CERT in detail by using a cell-free assay system for intermembrane transfer of lipids. CERT did not mediate the transfer of sphingosine or sphingomyelin at all. The activity of CERT to transfer saturated and unsaturated diacylglycerols, which structurally resemble ceramide, was 5-10% of the activity toward C(16)-ceramide. Among four stereoisomers of C(16)-ceramide, CERT specifically recognized the natural d-erythro isomer. CERT efficiently transferred ceramides having C(14), C(16), C(18), and C(20) chains, but not longer acyl chains, and also mediated efficient transfer of C(16)-dihydroceramide and C(16)-phyto-ceramide. Binding assays showed that CERT also recognizes short chain fluorescent analogs of ceramide with a stoichiometry of 1:1. Moreover, (1R,3R)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecamide, which inhibited the CERT-dependent pathway of ceramide trafficking in intact cells, was found to be an antagonist of the CERT protein. These results indicate that CERT can mediate transfer of various types of ceramides that naturally exist and their close relatives.
Kumagai
Keigo
K
Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640 and Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Yasuda
Satoshi
S
Okemoto
Kazuo
K
Nishijima
Masahiro
M
Kobayashi
Shu
S
Hanada
Kentaro
K
D001692:Biological Transport; D002474:Cell-Free System; D002518:Ceramides / Q000138:chemical synthesis / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D002518:Ceramides; D008024:Ligands; C119090:CERT1 protein, human; D017346:Protein Serine-Threonine Kinases