Neutral Lipid Metabolism Influences Phospholipid Synthesis and Deacylation in Saccharomyces cerevisiae

Gabriel Mora,Martin Fulda,Michael Scharnewski,Christopher Beh

doi:10.1371/journal.pone.0049269

Abstract

Establishment and maintenance of equilibrium in the fatty acid (FA) composition of phospholipids (PL) requires both regulation of the substrate available for PL synthesis (the acyl-CoA pool) and extensive PL turnover and acyl editing. In the present study, we utilize acyl-CoA synthetase (ACS) deficient cells, unable to recycle FA derived from lipid deacylation, to evaluate the role of several enzymatic activities in FA trafficking and PL homeostasis in Saccharomyces cerevisiae. The data presented show that phospholipases B are not contributing to constitutive PL deacylation and are therefore unlikely to be involved in PL remodeling. In contrast, the enzymes of neutral lipid (NL) synthesis and mobilization are central mediators of FA trafficking. The phospholipid:DAG acyltransferase (PDAT) Lro1p has a substantial effect on FA release and on PL equilibrium, emerging as an important mediator in PL remodeling. The acyl-CoA dependent biosynthetic activities of NL metabolism are also involved in PL homeostasis through active modulation of the substrate available for PL synthesis. In addition TAG mobilization makes an important contribution, especially in cells from stationary phase, to FA availability. Beyond its well-established role in the formation of a storage pool, NL metabolism could play a crucial role as a mechanism to uncouple the pools of PL and acyl-CoAs from each other and thereby to allow independent regulation of each one.

Highlights

The pathways for de novo PL synthesis are well understood [1,2], and most of the complex mechanisms that regulate the flow of metabolites through phosphatidic acid (PA) into the synthesis of different PL classes are elucidated [3,4]
While it is a well known fact that lipid turnover is a common process in cells and that it plays a major role in attaining the steady state lipid composition of the cell, the results obtained upon deletion of the acyl-CoA synthetases highlight the actual magnitude of the phenomena: by late stationary phase the cells have turned over an amount of fatty acid (FA) corresponding to four times their total content of esterified FA
Given that in WT cells these FA are activated and can reenter lipid metabolism, it becomes clear that lipid turnover and FA recycling make a major contribution to the acyl-CoA pool in addition to de novo FA synthesis

Summary

Introduction

The pathways for de novo PL synthesis are well understood [1,2], and most of the complex mechanisms that regulate the flow of metabolites through phosphatidic acid (PA) into the synthesis of different PL classes are elucidated [3,4]. The FA specificity of the enzymes involved in the biosynthesis is not sufficient and as an additional parameter the regulation of the acyl-CoA pool composition might be required. This is in part accomplished through control of de novo FA synthesis [9,10]. It begins to become clear that NL metabolism plays a central role within the mechanisms regulating the acyl-CoA pool [12,13] and can have a direct incidence on PL synthesis. The enzymes Are1p and Are2p make a minor contribution to acyl-CoA dependent TAG synthesis [17]; their main role, is the synthesis of SE [19,20]. SE hydrolysis, releasing a FFA and a sterol molecule, depends on the proteins Yeh1p, Yeh2p and Tgl1p [28,29,30]

Methods

Results

Conclusion