Hanada Kentaro, Kumagai Keigo, Yasuda Satoshi, Miura Yukiko, Kawano Miyuki, Fukasawa Masayoshi, Nishijima Masahiro
Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, 1-23-1, Toyama, Shinjuku-ku, Tokyo 162-8640, Japan.
Nature. 2003 Dec 18;426(6968):803-9. doi: 10.1038/nature02188.
Synthesis and sorting of lipids are essential for membrane biogenesis; however, the mechanisms underlying the transport of membrane lipids remain little understood. Ceramide is synthesized at the endoplasmic reticulum and translocated to the Golgi compartment for conversion to sphingomyelin. The main pathway of ceramide transport to the Golgi is genetically impaired in a mammalian mutant cell line, LY-A. Here we identify CERT as the factor defective in LY-A cells. CERT, which is identical to a splicing variant of Goodpasture antigen-binding protein, is a cytoplasmic protein with a phosphatidylinositol-4-monophosphate-binding (PtdIns4P) domain and a putative domain for catalysing lipid transfer. In vitro assays show that this lipid-transfer-catalysing domain specifically extracts ceramide from phospholipid bilayers. CERT expressed in LY-A cells has an amino acid substitution that destroys its PtdIns4P-binding activity, thereby impairing its Golgi-targeting function. We conclude that CERT mediates the intracellular trafficking of ceramide in a non-vesicular manner.
脂质的合成与分选对于膜生物发生至关重要；然而，膜脂运输的潜在机制仍知之甚少。神经酰胺在内质网合成，并转运至高尔基体区室转化为鞘磷脂。在一种哺乳动物突变细胞系LY-A中，神经酰胺向高尔基体运输的主要途径在基因上存在缺陷。在此，我们确定CERT是LY-A细胞中存在缺陷的因子。CERT与Goodpasture抗原结合蛋白的一个剪接变体相同，是一种具有磷脂酰肌醇-4-单磷酸结合（PtdIns4P）结构域和一个推定的催化脂质转移结构域的胞质蛋白。体外实验表明，这个催化脂质转移的结构域能从磷脂双层中特异性提取神经酰胺。在LY-A细胞中表达的CERT存在一个氨基酸替换，破坏了其PtdIns4P结合活性，从而损害其靶向高尔基体的功能。我们得出结论，CERT以非囊泡方式介导神经酰胺的细胞内运输。
