CTP synthetase and its role in phospholipid synthesis in the yeast Saccharomyces cerevisiae

Abstract

CTP synthetase is a cytosolic-associated glutamine amidotransferase enzyme that catalyzes the ATPdependent transfer of the amide nitrogen from glutamine to the C-4 position of UTP to form CTP. In the yeast Saccharomyces cerevisiae, the reaction product CTP is an essential precursor of all membrane phospholipids that are synthesized via the Kennedy (CDP-choline and CDP-ethanolamine branches) and CDP-diacylglycerol pathways. The URA7 and URA8 genes encode CTP synthetase in S. cerevisiae, and the URA7 gene is responsible for the majority of CTP synthesized in vivo. The CTP synthetase enzymes are allosterically regulated by CTP product inhibition. Mutations that alleviate this regulation result in an elevated cellular level of CTP and an increase in phospholipid synthesis via the Kennedy pathway. The URA7-encoded enzyme is phosphorylated by protein kinases A and C, and these phosphorylations stimulate CTP synthetase activity and increase cellular CTP levels and the utilization of the Kennedy pathway. The CTPS1 and CTPS2 genes that encode human CTP synthetase enzymes are functionally expressed in S. cerevisiae, and rescue the lethal phenotype of the ura7Δ ura8Δ double mutant that lacks CTP synthetase activity. The expression in yeast has revealed that the human CTPS1-encoded enzyme is also phosphorylated and regulated by protein kinases A and C.

Regulation of CTP Synthase Filament Formation During DNA Endoreplication in Drosophila

“…Consistent with this interpretation, a special requirement for human CTP synthase1 (CTPS1) activity in DNA replication was revealed recently in receptor-mediated activation of T cells by anti-CD3 and anti-CD28 antibodies (Martin et al 2014). The synthesis of phospholipids for membrane expansion is controlled by the levels of CTP, and the research group of Jeffrey R. Peterson at Fox Chase Cancer Center, Philadelphia, has demonstrated a role for CTPsyn in regulating the phospholipid composition of Drosophila germline cells (Chang and Carman 2008;Strochlic et al 2014). Our results demonstrated that supplying the enzymatic activity of CTPsyn can restore endoreplication defects in Cbl mutant cells, indicating that Cbl may be involved in maintaining the nucleotide balance.…”

Microsporidian genome analysis reveals evolutionary strategies for obligate intracellular growth

“…Therefore, it is possible that microsporidia use Class I aldolase both in glycolysis and the pentose phosphate pathway, because this ''double-duty'' strategy would be an efficient use of the microsporidian enzymatic repertoire. Nematocida and other microsporidia have very limited biosynthetic and degradative capabilities, as compared with other fungi (see Supplemental Material) but have retained a gene that encodes CTP synthase, which converts UTP into CTP, a nucleotide used for RNA/DNA synthesis and lipid synthesis (Chang and Carman 2008). CTP synthase is also present in the reduced genome of C. trachomatis, which encodes an active CTP synthase despite being able to import CTP (Wylie et al 1996).…”

Regulation of phospholipid synthesis in yeast

“…CTP is essential for phospholipid synthesis; it is the direct precursor of the activated, energy-rich intermediates CDP-DAG, CDP-choline, and CDP-ethanolamine (6). CTP is also used as the phosphate donor for the synthesis of PA by the DGK1-encoded DAG kinase (39).…”

“…CTP is also used as the phosphate donor for the synthesis of PA by the DGK1-encoded DAG kinase (39). Because the cellular levels of CTP are primarily controlled by product inhibition of CTP synthetase activity, expression of a mutant enzyme lacking this regulation results in elevated levels of CTP as well as an increased rate of PA synthesis and the derepression of UAS INO -containing genes (6,40). The increase in PA content and the inactivation of Opi1 repressor function (39) may result from the stimulation of DAG kinase activity by increased availability of its substrate CTP.…”

“…Moreover, the purification and characterization of several key phospholipid synthesis enzymes have led to an understanding of the biochemical regulation of phospholipid synthesis (1,4,5). In S. cerevisiae, phospholipid synthesis is a complex process that is regulated by both genetic and biochemical mechanisms (1,(3)(4)(5)(6)(7)(8)(9). The expression of phospholipid synthesis genes is controlled at the levels of transcription and mRNA stability (1,3,10).…”