Phosphatidate phosphatases (PAH) play a central role in lipid metabolism and intracellular signaling. Herein, we report thepresence of a low-molecular-weight PAH homolog in the single-celled ciliate Tetrahymena thermophila. In vitro phosphataseassay showed that TtPAH2 belongs to the magnesium-dependent phosphatidate phosphatase (PAP1) family. Loss offunction of TtPAH2 did not affect the growth of Tetrahymena. Unlike other known PAH homologs, TtPAH2 did not regulatelipid droplet number and ER morphology. TtPAH2 did not rescue growth and ER/nuclear membrane defects of the pah1Dyeast cells, suggesting that the phosphatidate phosphatase activity of the protein is not sufficient to perform these cellularfunctions. Surprisingly, TtPAH2 complemented the respiratory defect in the pah1D yeast cells indicating a specific role ofTtPAH2 in respiration. Overall, our results indicate that TtPAH2 possesses the minimal function of PAH protein family inrespiration. We suggest that the amino acid sequences absent from TtPAH2 but present in all other known PAH homologsare critical for lipid homeostasis and membrane biogenesis.
Volume 45, 2020
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