The product of the open reading frame YPL206c, Pgc1p, of the yeast Saccharomyces cerevisiae displays homology to bacterial and mammalian glycerophosphodiester phosphodiesterases. Deletion of PGC1 causes an accumulation of the anionic phospholipid, phosphatidylglycerol (PG), especially under conditions of inositol limitation. This PG accumulation was not caused by increased production of phosphatidylglycerol phosphate or by decreased consumption of PG in the formation of cardiolipin, the end product of the pathway. PG accumulation in the pgc1⌬ strain was caused rather by inactivation of the PG degradation pathway. Our data demonstrate an existence of a novel regulatory mechanism in the cardiolipin biosynthetic pathway in which Pgc1p is required for the removal of excess PG via a phospholipase C-type degradation mechanism. Cardiolipin (CL)2 is a major mitochondrial anionic phospholipid with important functions in promoting cell growth, anaerobic metabolism, mitochondrial function, and biogenesis (1, 2). Phosphatidylglycerol is not only a metabolic precursor in the biosynthetic pathway leading to the formation of cardiolipin but itself is an important phospholipid; for example it is the sole phospholipid of thylakoid membranes of prokaryotic and eukaryotic oxygenic photosynthetic organisms (3). In mammals, PG is especially important in pulmonary surfactant, an essential fluid produced by alveolar type II cells that covers the entire surface of the lung (4). Considering the importance of this anionic phospholipid, little is known about the mechanisms by which eukaryotic cells control PG membrane composition.In yeast cells, PG is a low abundance phospholipid, present at best as a few tenths of a percent of total cellular phospholipids, even under the conditions of respiratory growth (5). Therefore, PG is considered to be mainly a metabolic precursor to CL. Biosynthesis of CL starts with common intermediates of phospholipid biosynthesis, phosphatidic acid and CDP-diacylglycerol (DAG) (Fig. 1). Phosphatidylglycerol phosphate (PGP) is formed from CDP-DAG and glycerol 3-phosphate. This step is catalyzed by PGP synthase, product of the PGS1/PEL1 gene (6, 7). PGP is subsequently dephosphorylated to form PG. Finally, CL is synthesized in yeast and other eukaryotic organisms from CDP-DAG and PG via a reaction catalyzed by cardiolipin synthase (CRD1) (5,8,9). It is important to note that both CL and PG are subject to intense remodeling subsequent to their de novo synthesis (10).Mitochondrial phospholipid biosynthetic activities in general respond to factors affecting mitochondrial development and function, such as carbon source, growth phase, availability of oxygen, and mutations affecting mitochondrial development and function (11,12). In fact, both enzymatic activities of the CL biosynthetic pathway, PGP synthase and CL synthase, respond to mitochondrial development factors in such a way as to increase the production of CL when cells switch from fermentative to respiratory growth (13-15). A typical feature of yeast phosphol...

Although the 20-amino acid presequence present in 15-kDa pro-sterol carrier protein-2 (pro-SCP-2, the precursor of the mature 13-kDa SCP-2) alters the function of SCP-2 in lipid metabolism, the molecular basis for this effect is unresolved. The presequence dramatically altered SCP-2 structure as determined by circular dichroism, mass spectroscopy, and antibody accessibility such that pro-SCP-2 had 3-fold less ␣-helix, 7-fold more ␤-structure, 6-fold more reactive C terminus to carboxypeptidase A, 2-fold less binding of anti-SCP-2, and did not enhance sterol transfer from plasma membranes. These differences were not due to protein stability since (i) the same concentration of guanidine hydrochloride was required for 50% unfolding, and (ii) the ligand binding sites displayed the same high affinity (7) approaches revealed additional potential roles for SCP-2 in cellular fatty acid metabolism. However, resolving the relative roles of SCP-2 in cholesterol versus fatty acid metabolism has been complicated by the fact that neither the function of the 20-amino acid presequence in 15-kDa pro-SCP-2, the primary SCP-2 gene product, nor how it affects the intracellular targeting of this protein are yet known. Further, little is known about the structure and function pro-SCP-2 because it is posttranslationally completely cleaved to the mature SCP-2 in all tissues examined (reviewed in Ref.2). In addition, pro-SCP-2 is completely (8) or nearly completely cleaved to SCP-2 in cells transfected with the cDNA encoding pro-SCP-2 (9, 10). SCP-2 was originally isolated from liver and other tissues as a 13-kDa soluble protein whose amino acid sequence did not identify any consensus sequences targeting SCP-2 to specific intracellular organelle(s), suggesting a primarily cytosolic localization (11, 12). In contrast, cDNA sequencing revealed that the two SCP-2 gene products, 58-kDa SCP-x and 15-kDa pro-SCP-2, as well as the mature 13-kDa SCP-2 contained an C-terminal SKL peroxisomal targeting sequence, thereby suggesting an exclusive peroxisomal localization (reviewed in Refs. 2 and 13). However, immunogold electron microscopy and immunofluorescence imaging showed that, whereas SCP-x appears almost exclusively peroxisomal, the intracellular localization of SCP-2 is more complex with over half of the total SCP-2 being extraperoxisomal where it is localized diffusely in the cytoplasm as well as associated with endoplasmic reticulum and mitochondria (reviewed in Refs. 2, 3, and 13). The fact that the SCP-x and SCP-2 did not copurify with peroxisomes (catalase) in subcellular fractionation further supported differential intracellular distribution of SCP-2 in the cell.These studies suggest that the 20-amino acid presequence of the pro-SCP-2 may function in some manner to modify the intracellular targeting of this gene product and thereby account for dual functions of SCP-2 gene products in both fatty acid and sterol metabolism. Consistent with this possibility, transfection of cells with the cDNA encoding pro-SCP-2 (8 -10, 14, 15) alters ch...

Pdr16p is considered a factor of clinical azole resistance in fungal pathogens. The most distinct phenotype of yeast cells lacking Pdr16p is their increased susceptibility to azole and morpholine antifungals. Pdr16p (also known as Sfh3p) of Saccharomyces cerevisiae belongs to the Sec14 family of phosphatidylinositol transfer proteins. It facilitates transfer of phosphatidylinositol (PI) between membrane compartments in in vitro systems. We generated Pdr16pE235A, K267A mutant defective in PI binding. This PI binding deficient mutant is not able to fulfill the role of Pdr16p in protection against azole and morpholine antifungals, providing evidence that PI binding is critical for Pdr16 function in modulation of sterol metabolism in response to these two types of antifungal drugs. A novel feature of Pdr16p, and especially of Pdr16pE235A, K267A mutant, to bind sterol molecules, is observed.