The Saccharomyces cerevisiae phosphatidylinositol-transfer protein effects a ligand-dependent inhibition of choline-phosphate cytidylyltransferase activity.
The Saccharomyces cerevisiae protein SEC14p is required for Golgi function and cell viability in vivo. This requirement is obviated by mutations that specifically inactivate the CDP-choline pathway for phosphatidylcholine biosynthesis. The biochemical basis for the in vivo relationship between SEC14p function and the CDP-choline pathway has remained obscure. We now report that SEC14p effects an in vivo depression of CDP-choline pathway activity by inhibiting choline-phosphate cytidylyltransferase (CCTase; EC 2.7.7.15), the rate-determining enzyme of the CDP-choline pathway. Moreover, this SEC14p-mediated inhibition of CCTase was recapitulated in vitro and was saturable. Finally, whereas the SEC14p-dependent inhibition of CCTase in vitro was markedly reduced under assay conditions that were expected to increase levels of phosphatidylinositol-bound SEC14p, assay conditions expected to increase levels of phosphatidylcholine-bound SEC14p resulted in significant potentiation of CCTase inhibition. The collective data suggest that the phosphatidylcholine-bound form of SEC14p effects an essential repression of CDP-choline pathway activity in Golgi membranes by inhibiting CCTase and that the phospholipid-binding/exchange activity of SEC14p represents a mechanism by which the regulatory activity of SEC14p is itself controlled.
Skinner
H B
HB
Department of Cell Biology, University of Alabama, Birmingham 35294-0005.
McGee
T P
TP
McMaster
C R
CR
Fry
M R
MR
Bell
R M
RM
Bankaitis
V A
VA
D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D019916:Choline-Phosphate Cytidylyltransferase; D003001:Cloning, Molecular; D003566:Cytidine Diphosphate Choline / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli; D005838:Genotype; D006056:Golgi Apparatus / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008565:Membrane Proteins; D008954:Models, Biological; D009713:Nucleotidyltransferases / Q000037:antagonists & inhibitors*; D010716:Phosphatidylinositols / Q000378:metabolism; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D008024:Ligands; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D011994:Recombinant Proteins; C118289:SEC24 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D003566:Cytidine Diphosphate Choline; D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase; D002794:Choline