Coordinate regulation of phospholipid biosynthesis by serine in Saccharomyces cerevisiae

Abstract

The addition of L-serine to inositol-containing growth medium repressed membrane-associated CDPdiacylglycerol synthase (CTP:phosphatidate cytidylyltransferase, EC 2.7.7.41) and phosphatidylserine synthase (CDPdiacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) activities and subunit levels in wild-type Saccharomyces cerevisiae. Enzyme activities and subunit levels were not repressed when inositol was absent from the growth medium. The addition of L-serine to the growth medium did not affect the phospholipid composition of wild-type cells. CDPdiacylglycerol synthase and phosphatidylserine synthase were not regulated in the S. cerevisiae inositol biosynthesis ino2, ino4, and opil regulatory mutants, suggesting that regulation by inositol plus L-serine is coupled to inositol synthesis. Inositol and L-serine did not affect the activities of purified CDPdiacylglycerol synthase and phosphatidylserine synthase. The addition of compounds structurally related to L-serine to the growth medium of wild-type cells also resulted in a repression of CDPdiacylglycerol synthase and phosphatidylserine synthase but only in the presence of inositol. Phosphatidylinositol synthase (CDPdiacylglycerol:myo-inositol 3-phosphatidyltransferase, EC 2.7.8.11) was not regulated by inositol plus L-serine.In Saccharomyces cerevisiae, several phospholipid biosynthetic enzymes in the reaction sequence phosphatidictidylcholine (PC) are regulated in a coordinate fashion. CDP-DG synthase (23), PS synthase (10, 27), PS decarboxylase (11), and the phospholipid N-methyltransferase (35, 36) activities are repressed in wild-type cells grown in medium supplemented with inositol plus choline. CDP-DG synthase (23) and PS synthase (34) activities are also repressed when wild-type cells are grown with inositol plus ethanolamine. PE and PC are synthesized via the CDP-ethanolamine-and CDP-choline-based pathways (25) when the cells are supplemented with ethanolamine and choline (2). Ethanolamine or choline has no effect on CDP-DG synthase (23), PS synthase (27, 34), and phospholipid N-methyltransferase (27, 36) activities in the absence of inositol. The addition of inositol alone to the growth medium causes a partial repression of CDP-DG synthase (23), PS synthase (27, 34), and the phospholipid N-methyltransferase (36) activities. However, phosphatidylinositol (PI) synthase, which uses inositol as a substrate, is not regulated in response to inositol, ethanolamine, and choline (17,27).Inositol-l-phosphate synthase is the cytoplasmicassociated enzyme responsible for inositol synthesis. This enzyme is repressed in wild-type cells by inositol and is derepressed in the absence of inositol (15). Mutants with lesions in genes whose wild-type products exert a positive (i.e., the ino2 and ino4 strains) or a negative (i.e., the opil strain) effect upon inositol-1-phosphate synthase expression (12,14,18,19) exert pleiotropic effects upon the coordinately regulated enzymes involved in the pathway leading to PC (4,23,26,27,32,34 the coordinate regulation of the en...

Reduction of CDP-diacylglycerol Synthase Activity Results in the Excretion of Inositol by Saccharomyces cerevisiae

“…CDP-DAG synthase activity is regulated by water-soluble precursors of phospholipid biosynthesis. Inclusion of inositol in growth medium reduces synthase activity, and this repressive effect is enhanced by the addition of ethanolamine or choline (12). The CDP-DAG synthase activity also decreases as cells enter the stationary phase in inositol-containing medium (13).…”

“…A UAS INO regulatory sequence is found in the 5Ј-untranslated region of the CDS1 gene. This unique sequence serves as a binding site for INO2 and INO4 gene products and thus mediates coordinated regulation of phospholipid biosynthetic gene expression (1, 18 -20), which may explain the decreased level of CDP-DAG synthase activity when yeast cells are supplied with inositol, choline, and ethanolamine in growth medium (12). The CDS1 gene encodes the majority, if not all, of the CDP-DAG synthase activity in yeast.…”

Regulation of CDP-diacylglycerol synthesis and utilization by inositol and choline in Schizosaccharomyces pombe

“…The level at which PGP synthase is regulated has not been determined, although degradation or inactivation of the enzyme is one likely mechanism (16). Repression of CDP-DG synthase is evident at the level of the Mr-56,000 subunit (21,28). Inositol-mediated repression of PS synthase is apparent at the level of the Mr-23,000 subunit (21,34) and its corresponding mRNA (2).…”

“…Repression of CDP-DG synthase is evident at the level of the Mr-56,000 subunit (21,28). Inositol-mediated repression of PS synthase is apparent at the level of the Mr-23,000 subunit (21,34) and its corresponding mRNA (2). Furthermore, inositol is a noncompetitive inhibitor of PS synthase (26).…”

“…synthesis (19). Expression of CDP-DG synthase (21,22,28), PS synthase (2,10,21,27,28,34), and PGP synthase (16) is repressed when wild-type cells are grown in inositol-containing (I+) medium. The level at which PGP synthase is regulated has not been determined, although degradation or inactivation of the enzyme is one likely mechanism (16).…”