Phosphorylation of the lipid droplet localized glycerol‑3‑phosphate acyltransferase Gpt2 prevents a futile triacylglycerol cycle in yeast

The proteome of lipid droplets, storage compartments of triacylglycerols (TAGs), comprises TAG synthesizing and TAG degrading enzymes. Thus, to prevent a futile cycle the activity of enzymes catalyzing key steps in TAG turnover has to be strictly coordinated. The first and committed reaction of TAG synthesis is catalyzed by a glycerol‑3‑phosphate acyltransferase (GPAT). Here we demonstrate that in the model organism yeast the lipid droplet associated GPAT Gpt2 requires phosphorylation at a conserved motif to prevent a futile TAG cycle. Phosphorylation deficiency at the conserved motif increases the enzyme activity of Gpt2 and consequently enhances TAG synthesis. In proliferating cells the phosphorylation deficient GPAT-form contributes to TAG metabolism similar to control. However, during lipolysis the increased activity of phosphorylation deficient Gpt2 causes a constant TAG level by using TAG-released fatty acids as substrate for TAG synthesis. These data strongly indicate that phosphorylation of Gpt2 at a conserved motif plays a critical role in coordinating the synthesis and degradation of TAGs. [Display omitted] •The glycerol‑3‑P acyltransferase Gpt2 is phosphorylated at a conserved motif.•Phosphorylation deficiency of Gpt2 at this motif increases its enzyme activity.•Expression of phosphorylation deficient Gpt2 increases the cellular TAG level.•Misregulated phosphorylation deficient Gpt2 causes a transient futile TAG cycle.