Four Acyltransferases Uniquely Contribute to Phospholipid Heterogeneity in Saccharomyces cerevisiae

Abstract

Diverse acyl‐CoA species and acyltransferase isoenzymes are part of a complex system that synthesizes glycerophospholipids and triacylglycerols. Saccharomyces cerevisiae, having four main acyl‐CoA species, two main glycerol‐3‐phosphate 1‐O‐acyltransferases (Gat1p, Gat2p) and two main 1‐acylglycerol‐3‐phosphate O‐acyltransferases (Lpt1p, Slc1p), provides an experimental system of reduced complexity. To comprehensively examine the in vivo contribution of the acyltransferase isoenzymes to phospholipid heterogeneity, haploid yeast with compound mutations were generated: gat1Δlpt1Δ, gat2Δlpt1Δ, gat1Δslc1Δ, and gat2Δslc1Δ. All mutations mildly reduced [3H]palmitic acid incorporation into phospholipids relative to triacylglycerol. Electrospray ionization tandem mass spectrometry analysis of phospholipids identified few differences from wild type in gat1Δlpt1Δ, dramatic differences in gat2Δslc1Δ, and intermediate changes in the other two mutants. The gat2Δslc1Δ yeast, solely expressing Gat1p and Lpt1p, had phospholipids with 10% more unsaturated acyl chains and 20% fewer species with 34 acyl chain carbons. These percent changes varied among phospholipid head group species. Thus, the combined activities of Gat2p and Slc1p seem to promote the production of phospholipids with “mixed” chain lengths (e.g. 16 and 18 carbons). This is particularly true for phosphatidylserine. Head group allocation was also affected in gat2Δslc1Δ yeast which had 15% more phosphatidylethanolamine, 38% less phosphatidylserine, and 85% less phosphatidylglycerol. These alterations slowed growth in rich media at 30 °C by 18% but not in media with non‐fermentable carbon sources. Growth was abrogated in rich media at 18.5 °C or containing 10% ethanol. Therefore, Gat2p and Slc1p primarily dictate appropriate phospholipid acyl chain composition, presumably through de novo synthesis, in several growth conditions. This composition is likely steered by Slc1p selectively pairing acyl chains of different lengths.