The lipid droplet protein Pgc1 controls the subcellular distribution of phosphatidylglycerol

Abstract

The biosynthesis of yeast phosphatidylglycerol (PG) takes place in the inner mitochondrial membrane. Outside mitochondria, the abundance of PG is low. Here, we present evidence that the subcellular distribution of PG is maintained by the locally controlled enzymatic activity of the PG-specific phospholipase, Pgc1. A fluorescently labeled Pgc1 protein accumulates on the surface of lipid droplets (LD). We show, however, that LD are not only dispensable for Pgc1-mediated PG degradation, but do not even host any phospholipase activity of Pgc1. Our in vitro assays document the capability of LD-accumulated Pgc1 to degrade PG upon entry to the membranes of the endoplasmic reticulum, mitochondria and even of artificial phospholipid vesicles. Fluorescence recovery after photobleaching analysis confirms the continuous exchange of GFP-Pgc1 within the individual LD in situ, suggesting that a steady-state equilibrium exists between LD and membranes to regulate the immediate phospholipase activity of Pgc1. In this model, LD serve as a storage place and shelter Pgc1, preventing its untimely degradation, while both phospholipase activity and degradation of the enzyme occur in the membranes.

Blocking phosphatidylglycerol degradation in yeast defective in cardiolipin remodeling results in a new model of the Barth syndrome cellular phenotype

“…Therefore, increased SE fraction in all the analyzed mutant strains, indicating a connection between PG and CL biosynthesis and lipid droplets, is not surprising. We showed before that Pgc1 localizes predominantly onto lipid droplets although the protein is active in membranes of endoplasmic reticulum and mitochondria (19). Increased lipid storage has been described as a frequent complication in TAZ1 deficient BTHS patients (12,41,42).…”

“…Intact mitochondria were isolated as described previously (17). The final mitochondrial pellet was suspended in the respiration buffer (0.6 M mannitol, 20 mM HEPES/KOH pH 7.1, 2 mM MgCl2, 1 mM EGTA, 0.1 % fatty acid-free bovine serum albumin, 10 mM KH2PO4) and used for measurement of O2 consumption, the activity of cytochrome c reductase, the activity of cytochrome c oxidase and ATP-hydrolase activity as described in (17) and measurement of Pgc1 activity as described in (19).…”

“…Phospholipid analysis was performed as described previously (19), fatty acids analysis, and western blot analysis as described in (17). Statistical comparisons were carried out by one-way J o u r n a l P r e -p r o o f analysis of variance using SigmaPlot 12 software (Systat Software, San Jose, CA).…”

“…PG level in yeast is controlled by PG-phosphate (PGP) synthase Pgs1 and PG-specific phospholipase Pgc1 through an effective mechanism capable of fast, wide-range, and bidirectional PG regulation (19). Deletion of PGC1 leads, under conditions of sustained Pgs1 activity, to nonspecific accumulation of PG without distinct side effects on the amounts of other phospholipids, including CL, but with apparent adverse effects on mitochondrial fusion and respiration (17).…”

Plasma Membrane Protein Nce102 Modulates Morphology and Function of the Yeast Vacuole

“…Several nutrient transporters of the yeast plasma membrane have been shown to accumulate in a specialized lateral microdomain, MCC (Membrane Compartment of arginine permease Can1) to prevent their ubiquitination and subsequent endocytosis in the absence of substrate [1][2][3]. Similarly, phosphatidylglycerol-specific phospholipase C, Pgc1, is activated and rapidly recognized by the endoplasmic reticulum-associated degradation (ERAD) pathway only after the release from the lipid droplet surface to the adjacent ER and/or outer mitochondrial membrane [4]. In stationary cells, cytosolic 5 -3 exoribonuclease Xrn1 is reversibly inactivated through binding at plasma membrane-associated, MCC-organizing protein complex, the eisosome [5,6].…”