Yeast sphingolipids do not need to contain very long chain fatty acids

Synthesis of VLCFAs (very long chain fatty acids) and biosynthesis of DHS (dihydrosphingosine) both are of vital importance for Saccharomyces cerevisiae. The bulb, of VLCFAs and DHS are used for ceramide synthesis by the Lag1p (longevity-assurance gene 1)/Lac1p (longevity-assurance gene cognate 1)/Lip1p (Lag1p/Lac1p interacting protein) ceramide synthase. LAG1 and LAC1 are redundant but LIP1 isessential. Here we show that 4 Delta (lag1 Delta lac1 Delta ypc1 Delta ydc1 Delta) cells devoid of all known endogenous ceramide synthesis pathways are unviable but can be rescued by the expression of Lass5, a mouse LAG1 homologue. Ceramide synthase activity of 4 Delta. Lass5 cells only utilizes C, and C-18 fatty acids and does not require the help of Lip1p, an essential cofactor of Lag1p/Lac1p. HPLC-electrospray ionization-MS/MS analysis demonstrated that in IPCs (inositolphosphorylceramides) of 4 Delta. Lass5, the very long chain fatty acids (C-26 and C-24) account for < I % instead of the normal > 97 %. Notwithstanding, IPCs incorporated into glycosylphosphatidylinositol anchors of 4 Delta.Lass5 show normal mobility on TLC and the ceramide and raft-dependent traffic of Gas1p (glycophospholipid-anchored surface protein) from endoplasmic reticulum to Golgi remains almost normal. Moreover, the biosynthesis of C-24:0 fatty acids remains essential. Thus, C-24:0 and dihydrosphingosine are both necessary for survival of yeast cells even if they utilize C-16 and C-18 fatty acids for sphingolipid biosynthesis.