Stock S D, Hama H, Radding J A, Young D A, Takemoto J Y
Department of Biology, Utah State University, Logan, Utah 84322-5305, USA.
Antimicrob Agents Chemother. 2000 May;44(5):1174-80. doi: 10.1128/AAC.44.5.1174-1180.2000.
Syringomycin E is an antifungal cyclic lipodepsinonapeptide that inhibits the growth of Saccharomyces cerevisiae by interaction with the plasma membrane. A screen conducted to find the yeast genes necessary for its fungicidal action identified two novel syringomycin E response genes, SYR3 and SYR4. A syr3 mutant allele was complemented by ELO2 and ELO3. These genes encode enzymes that catalyze the elongation of sphingolipid very long chain fatty acids. Tetrad analysis showed that SYR3 was ELO2. Strains with deletions of SYR3/ELO2 and ELO3 were resistant to syringomycin E, and lipid analyses of both mutants revealed shortened fatty acid chains and lower levels of sphingolipids. SYR4 was identified by Tn5 inactivation of genomic library plasmids that complemented a syr4 mutant allele. SYR4 was found to be identical to IPT1, which encodes the terminal sphingolipid biosynthetic enzyme, mannosyl-diinositolphosphoryl-ceramide synthase. Deletion Deltasyr4/ipt1 strains were viable, were resistant to syringomycin E, did not produce mannosyl-diinositolphosphoryl-ceramide, and accumulated mannosyl-inositolphosphoryl-ceramide. Accumulation of mannosyl-inositolphosphoryl-ceramide was not responsible for resistance since a temperature-sensitive secretory pathway mutant (sec14-3(ts)) accumulated this sphingolipid and was sensitive to syringomycin E. Finally, Deltacsg1/sur1 and Deltacsg2 strains defective in the transfer of mannose to inositolphosphoryl-ceramide were resistant to syringomycin E. These findings show that syringomycin E growth inhibition of yeast is promoted by the production of sphingolipids with fully elongated fatty acid chains and the mannosyl and terminal phosphorylinositol moieties of the polar head group.
丁香霉素E是一种抗真菌的环状脂肽缩酚酸肽，它通过与质膜相互作用来抑制酿酒酵母的生长。为寻找其杀菌作用所必需的酵母基因而进行的一项筛选鉴定出了两个新的丁香霉素E反应基因SYR3和SYR4。一个syr3突变等位基因由ELO2和ELO3互补。这些基因编码催化鞘脂超长链脂肪酸延长的酶。四分体分析表明SYR3就是ELO2。缺失SYR3/ELO2和ELO3的菌株对丁香霉素E具有抗性，对这两种突变体的脂质分析显示脂肪酸链缩短且鞘脂水平降低。SYR4是通过对互补syr4突变等位基因的基因组文库质粒进行Tn5失活鉴定出来的。发现SYR4与IPT1相同，IPT1编码末端鞘脂生物合成酶甘露糖基 - 二肌醇磷酸神经酰胺合酶。缺失Δsyr4/ipt1的菌株是有活力的，对丁香霉素E具有抗性，不产生甘露糖基 - 二肌醇磷酸神经酰胺，并积累甘露糖基 - 肌醇磷酸神经酰胺。甘露糖基 - 肌醇磷酸神经酰胺的积累并不导致抗性，因为一个温度敏感的分泌途径突变体（sec14 - 3(ts)）积累了这种鞘脂并且对丁香霉素E敏感。最后，在甘露糖向肌醇磷酸神经酰胺转移方面有缺陷的Δcsg1/sur1和Δcsg2菌株对丁香霉素E具有抗性。这些发现表明，酵母中丁香霉素E的生长抑制作用是由具有完全延长的脂肪酸链以及极性头部基团的甘露糖基和末端磷酸肌醇部分的鞘脂的产生所促进的。
