Loss of hydroxyl groups from the ceramide moiety can modify the lateral diffusion of membrane proteins in S. cerevisiae

In the yeast Saccharomyces cerevisiae , structural diversities of complex sphingolipids [inositol phosphorylceramide (IPC), mannosylinositol phosphorylceramide, and mannosyldiinositol phosphorylceramide] are often observed in the presence or absence of hydroxyl groups on the C-4 position of long-chain base (C4-OH) and the C-2 position of very long-chain fatty acids (C2-OH), but the biological signifi - cance of these groups remains unclear. Here, we evaluated cellular membrane fl uidity in hydroxyl group-defective yeast mutants by fl uorescence recovery after photobleaching. The lateral diffusion of enhanced green fl uorescent proteintagged hexose transporter 1 (Hxt1-EGFP) was infl uenced by the absence of C4-OH and/or C2-OH. Notably, the fl uorescence recovery of Hxt1-EGFP was dramatically decreased in the sur2 - mutant (absence of C4-OH) under the csg1 - csh1 - background, in which mannosylation of IPC is blocked leading to IPC accumulation, while the recovery in the scs7 - mutant (absence of C2-OH) under the same background was modestly decreased. In addition, the amount of low affi nity tryptophan transporter 1 (Tat1)-EGFP was markedly decreased in the sur2 - csg1 - csh1 - mutant and accumulated in intracellular membranes in the scs7 - csg1 - csh1 - mutant without altering its protein expression. These results suggest that C4-OH and C2-OH are most probably critical factors for maintaining membrane fl uidity and proper turnover of membrane molecules in yeast containing complex sphingolipids with only one hydrophilic head group. -Uemura, S., F. Shishido, M. Tani, T. Mochizuki, F. Abe, and J-i. Inokuchi. Loss of hydroxyl groups from the ceramide moiety can modify the lateral diffusion of membrane proteins in S. cerevisiae . J. Lipid Res. 2014. 55: 1343 - 1356 .