A Lipid-mediated Quality Control Process in the Golgi Apparatus in Yeast

Abstract

When heme biosynthesis is disrupted, the yeast Saccharomyces cerevisiae becomes unable to synthesize its major sterol, ergosterol, and desaturate fatty acids. We took advantage of this physiological peculiarity to evaluate the consequences of ergosterol and/or unsaturated fatty acid (UFA) depletions on the biogenesis of a model polytopic plasma membrane protein, the uracil permease Fur4p. We show that under UFA shortage, which results in low amounts of diunsaturated phospholipid species, and under ergosterol depletion, Fur4p is prematurely routed from the Golgi apparatus to the vacuolar lumen in a process that requires the ubiquitin ligase Rsp5p. Interestingly, this diversion is not correlated to Fur4p exclusion from detergent-resistant membranes. In an independent set of experiments, we show that Fur4p targeting to the plasma membrane depends on phosphatidylethanolamine amounts and more specifically on the propensity of this phospholipid to form a hexagonal phase. In light of recent literature, we propose a model in which ergosterol and diunsaturated phospholipid species maintain optimal membrane curvature for Fur4p to evade the Golgi quality control process and to be properly delivered to its normal destination.

The lateral compartmentation of the yeast plasma membrane

“…The intracellular trafficking of all MCC-specific transporters recognized so far depends on ergosterol biosynthesis [9,17,24,32]. For Can1, in addition, the phosphatidyl ethanolamine was shown to be required for correct delivery of the permease to the plasma membrane [23].…”

Targeting surface voids to counter membrane disorders in lipointoxication-related diseases

“…3D). Given that a 40% saturation ratio is enough to preclude yeast cell growth (Pineau et al, 2008), we conclude from these experiments that, in contrast to OLPA, the effects of OAG on alleviating SFA lipointoxication cannot be accounted for by a simple restoration of the phospholipid content. However, the enrichment of 34:1 lipid species revealed that some of the OAG Ole chains are hydrolyzed and redistributed within phospholipids to form monounsaturated (one double bond) species Figs S2A and S3).…”

“…When grown in the absence of δ-ALA, this strain fails to synthesize heme, the prosthetic group of Ole1p, the fatty acid desaturase. As a consequence, the hem1Δ cells stop growing as early as 5 h after a shift to non-δ-ALA supplemented medium [YPD+ergosterol (Erg), denoted Ø] and this arrest correlates with an accumulation of SFA [mainly myristic (C14:0), palmitic (C16:0) and stearic (C18:0) acids] at the expense of unsaturated fatty acids [UFAs; palmitoleic (C16:1) and oleic (C18:1) acids] (Ferreira et al, 2004;Pineau et al, 2008). Interestingly, cell growth can be fully recovered and all the trademarks of SFA lipointoxication alleviated if selective UFAs, such as the mono-unsaturated fatty acid oleic acid (Ole), are added to the medium [ (Deguil et al, 2011); Table S1 and Fig.…”

The “Raman spectroscopic signature of life” is closely related to haem function in budding yeasts

“…We have measured 30 different cells from 6 independent batches of culture and none of the hem1D yeasts showed the "Raman spectroscopic signature of life" at 1602 cm À1 . The strain also displays growth arrest at early stage so that its OD 600 never reaches the same level as wild type strains or hem1D strain supplied with ALA (data not shown, refer to [11]). This result is consistent with our expectation that the 1602 cm À1 signal is closely related to haem function.…”

“…The image and Raman spectra of wild type and hem1D yeasts compared with squalene vided with d-aminolevulinate (ALA), the product of ALA synthase, or both ergosterol and unsaturated fatty acids [11]. Therefore, it is clear that hem1D yeasts are truly deficient in haem biosynthesis and no other metabolic pathways could compensate for it.…”