Edited by George M. CarmanPhospholipase B-mediated hydrolysis of phosphatidylcholine (PC) results in the formation of free fatty acids and glycerophosphocholine (GPC) in the yeast Saccharomyces cerevisiae. GPC can be reacylated by the glycerophosphocholine acyltransferase Gpc1, which produces lysophosphatidylcholine (LPC), and LPC can be converted to PC by the lysophospholipid acyltransferase Ale1. Here, we further characterized the regulation and function of this distinct PC deacylation/reacylation pathway in yeast. Through in vitro and in vivo experiments, we show that Gpc1 and Ale1 are the major cellular GPC and LPC acyltransferases, respectively. Importantly, we report that Gpc1 activity affects the PC species profile. Loss of Gpc1 decreased the levels of monounsaturated PC species and increased those of diunsaturated PC species, whereas Gpc1 overexpression had the opposite effects. Of note, Gpc1 loss did not significantly affect phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine profiles. Our results indicate that Gpc1 is involved in postsynthetic PC remodeling that produces more saturated PC species. qRT-PCR analyses revealed that GPC1 mRNA abundance is regulated coordinately with PC biosynthetic pathways. Inositol availability, which regulates several phospholipid biosynthetic genes, down-regulated GPC1 expression at the mRNA and protein levels and, as expected, decreased levels of monounsaturated PC species. Finally, loss of GPC1 decreased stationary phase viability in inositol-free medium. These results indicate that Gpc1 is part of a postsynthetic PC deacylation/reacylation remodeling pathway (PC-DRP) that alters the PC species profile, is regulated in coordination with other major lipid biosynthetic pathways, and affects yeast growth.

Phosphatidylcholine (PC) is the most abundant glycerophospholipid found in most eukaryotic membranes. Changes in its synthesis, turnover and remodeling play a crucial role in maintaining membrane homeostasis. PC species vary depending upon the acyl chains attached at the sn‐1 and sn‐2 position of the glycerol backbone. The fatty acid components of yeast PC are relatively simple, consisting of mostly C16:0, C16:1, C18:0 and C18:1 combined to produce PC species in which either one or both acyl chains is monounsaturated. Thus, the four major PC species found in yeast consist predominantly of the following chain combinations: two C16:1 to produce 32:2 PC, C16:0 and C16:1 to produce 32:1PC, C16:1 and C18:1 to produce 34:2PC, C16:0 and C18:1 or 18:0 and C16;1 to produce 34:1PC. Acyl chain composition is important as it affects the physical properties of membranes such as thickness, curvature and fluidity. We have recently reported on the characterization of glycerophosphocholine acyltransferase, Gpc1. Gpc1 acylates glycerophosphocholine (GPC), the product of the complete deacylation of PC, to produce lysophosphatidylcholine (LysoPC). LysoPC can then be converted to PC by the lysophospholipd acyltransferase, Ale1. In order to investigate the role of Gpc1 in PC remodeling, we performed PC species analyses on strains lacking or overexpressing GPC1. Our data indicates that the loss of GPC1 results in a decrease in PC species with a single unsaturation (32:1 and 34:1) and an increase in PC species with two unsaturations (32:2 and 34:2). Conversely, the overexpression of GPC1 results in an increase in singly unsaturated PC species (32:1 and 34:1). Expression analyses indicate that the GPC1 is upregulated upon attenuation of PC and sphingolipid biosynthetic pathways. Finally, preliminary phenotypic studies indicate that while loss of GPC1 does not affect log phase doubling time, it does result in a decrease in long‐term cell survival. Overall, we provide evidence that the remodeling of PC to more saturated species by Gpc1 is regulated in coordination with other lipid biosynthetic pathways and impacts stationary phase cell viability.Support or Funding InformationWe acknowledge support from National Institute of Health Grant NIH R15 GM104876 and Duquesne University.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.