Hornemann Thorsten, Penno Anke, Rütti Markus F, Ernst Daniela, Kivrak-Pfiffner Fatma, Rohrer Lucia, von Eckardstein Arnold
Institute for Clinical Chemistry, University Hospital Zurich, CH-8091 Zurich, Switzerland.
J Biol Chem. 2009 Sep 25;284(39):26322-30. doi: 10.1074/jbc.M109.023192. Epub 2009 Aug 1.
The enzyme serine palmitoyltransferase (SPT) catalyzes the rate-limiting step in the de novo synthesis of sphingolipids. Previously the mammalian SPT was described as a heterodimer composed of two subunits, SPTLC1 and SPTLC2. Recently we identified a novel third SPT subunit (SPTLC3). SPTLC3 shows about 68% identity to SPTLC2 and also includes a pyridoxal phosphate consensus motif. Here we report that the overexpression of SPTLC3 in HEK293 cells leads to the formation of two new sphingoid base metabolites, namely C(16)-sphinganine and C(16)-sphingosine. SPTLC3-expressing cells have higher in vitro SPT activities with lauryl- and myristoyl-CoA than SPTLC2-expressing cells, and SPTLC3 mRNA expression levels correlate closely with the C(16)-sphinganine synthesis rates in various human and murine cell lines. Approximately 15% of the total sphingolipids in human plasma contain a C(16) backbone and are found in the high density and low density but not the very low density lipoprotein fraction. In conclusion, we show that the SPTLC3 subunit generates C(16)-sphingoid bases and that sphingolipids with a C(16) backbone constitute a significant proportion of human plasma sphingolipids.
丝氨酸棕榈酰转移酶（SPT）催化鞘脂从头合成中的限速步骤。此前，哺乳动物SPT被描述为由两个亚基SPTLC1和SPTLC2组成的异二聚体。最近，我们鉴定出一种新的第三个SPT亚基（SPTLC3）。SPTLC3与SPTLC2具有约68%的同一性，并且还包含一个磷酸吡哆醛共有基序。在此我们报告，在HEK293细胞中过表达SPTLC3会导致形成两种新的鞘氨醇碱代谢产物，即C(16)-鞘氨醇和C(16)-鞘氨醇。与表达SPTLC2的细胞相比，表达SPTLC3的细胞对月桂酰辅酶A和肉豆蔻酰辅酶A具有更高的体外SPT活性，并且SPTLC3 mRNA表达水平与各种人和小鼠细胞系中的C(16)-鞘氨醇合成速率密切相关。人血浆中约15%的总鞘脂含有C(16)主链，并且存在于高密度脂蛋白和低密度脂蛋白部分，但不存在于极低密度脂蛋白部分。总之，我们表明SPTLC3亚基产生C(16)-鞘氨醇碱，并且具有C(16)主链的鞘脂在人血浆鞘脂中占很大比例。
