Selective Disruption of Phosphatidylcholine Metabolism of the Intracellular Parasite Toxoplasma gondii Arrests Its Growth

Abstract

Toxoplasma gondii is an intracellular protozoan parasite capable of causing devastating infections in immunocompromised and immunologically immature individuals. In this report, we demonstrate the relative independence of T. gondii from its host cell for aminoglycerophospholipid synthesis. The parasite can acquire the lipid precursors serine, ethanolamine, and choline from its environment and use them for the synthesis of its major lipids, phosphatidylserine (PtdSer), phosphatidylethanolamine (PtdEtn), and phosphatidylcholine (PtdCho), respectively. Dimethylethanolamine (Etn(Me)2), a choline analog, dramatically interfered with the PtdCho metabolism of T. gondii and caused a marked inhibition of its growth within human foreskin fibroblasts. In tissue culture medium supplemented with 2 mm Etn(Me)2, the parasite-induced lysis of the host cells was dramatically attenuated, and the production of parasites was inhibited by more than 99%. The disruption of parasite growth was paralleled by structural abnormalities in its membranes. In contrast, no negative effect on host cell growth and morphology was observed. The data also reveal that the Etn(Me)2-supplemented parasite had a time-dependent decrease in its PtdCho content and an equivalent increase in phosphatidyldimethylethanolamine, whereas other major lipids, PtdSer, PtdEtn, and PtdIns, remained largely unchanged. Relative to host cells, the parasites incorporated more than 7 times as much Etn(Me)2 into their phospholipid. These findings reveal that Etn(Me)2 selectively alters parasite lipid metabolism and demonstrate how selective inhibition of PtdCho synthesis is a powerful approach to arresting parasite growth. Toxoplasma gondii is an intracellular protozoan parasite capable of causing devastating infections in immunocompromised and immunologically immature individuals. In this report, we demonstrate the relative independence of T. gondii from its host cell for aminoglycerophospholipid synthesis. The parasite can acquire the lipid precursors serine, ethanolamine, and choline from its environment and use them for the synthesis of its major lipids, phosphatidylserine (PtdSer), phosphatidylethanolamine (PtdEtn), and phosphatidylcholine (PtdCho), respectively. Dimethylethanolamine (Etn(Me)2), a choline analog, dramatically interfered with the PtdCho metabolism of T. gondii and caused a marked inhibition of its growth within human foreskin fibroblasts. In tissue culture medium supplemented with 2 mm Etn(Me)2, the parasite-induced lysis of the host cells was dramatically attenuated, and the production of parasites was inhibited by more than 99%. The disruption of parasite growth was paralleled by structural abnormalities in its membranes. In contrast, no negative effect on host cell growth and morphology was observed. The data also reveal that the Etn(Me)2-supplemented parasite had a time-dependent decrease in its PtdCho content and an equivalent increase in phosphatidyldimethylethanolamine, whereas other major lipids, PtdSer, PtdEtn, and PtdIns, remained largely unchanged. Relative to host cells, the parasites incorporated more than 7 times as much Etn(Me)2 into their phospholipid. These findings reveal that Etn(Me)2 selectively alters parasite lipid metabolism and demonstrate how selective inhibition of PtdCho synthesis is a powerful approach to arresting parasite growth. Toxoplasma gondii is a ubiquitous, obligate intracellular protozoan parasite capable of infecting virtually all types of nucleated mammalian and avian cells (1Tenter A.M. Heckeroth A.R. Weiss L.M. Int. J. Parasitol. 2000; 30: 1217-1258Crossref PubMed Scopus (2366) Google Scholar). As an opportunistic human pathogen, T. gondii is an important cause of disease in immunocompromised individuals (2Luft B.J. Hafner R. Korzun A.H. Leport C. Antoniskis D. Bosler E.M. Bourland D.D. II I Uttamchandani R. Fuhrer J. Jacobson J. Morlat P. Vilde J-L. Remington J.S. N. Engl. J. Med. 1993; 329: 995-1000Crossref PubMed Scopus (366) Google Scholar) and in neonates following congenital infection (3Wong S.Y. Remington J.S. Clin. Infect. Dis. 1994; 18: 853-862Crossref PubMed Scopus (316) Google Scholar). Upon invasion of a host cell, the parasite resides in a specialized compartment, the parasitophorous vacuole (PV), 1The abbreviations used are: PV, parasitophorous vacuole; PtdSer, phosphatidylserine; PtdEtn, phosphatidylethanolamine; PtdCho, phosphatidylcholine; Etn(Me)2, N,N-dimethylethanolamine; PtdEtn(Me)2, phosphatidyldimethylethanolamine; MEM, minimal essential medium; HFF, human foreskin fibroblast; Etn, ethanolamine; Cho, choline; TLC, thin layer chromatography; PtdIns, phosphatidylinositol; PtdOH, phosphatidic acid; PBS, phosphate-buffered saline; PMSF, phenylmethyl-sulfonyl fluoride; EST, expressed sequence tag. 1The abbreviations used are: PV, parasitophorous vacuole; PtdSer, phosphatidylserine; PtdEtn, phosphatidylethanolamine; PtdCho, phosphatidylcholine; Etn(Me)2, N,N-dimethylethanolamine; PtdEtn(Me)2, phosphatidyldimethylethanolamine; MEM, minimal essential medium; HFF, human foreskin fibroblast; Etn, ethanolamine; Cho, choline; TLC, thin layer chromatography; PtdIns, phosphatidylinositol; PtdOH, phosphatidic acid; PBS, phosphate-buffered saline; PMSF, phenylmethyl-sulfonyl fluoride; EST, expressed sequence tag. a unique and dynamic nonfusogenic membrane organelle (4Suss-Toby E. Zimmerberg J. Ward G.E. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 8413-8418Crossref PubMed Scopus (240) Google Scholar, 5Sinai A.P. Joiner K.A. Annu. Rev. Microbiol. 1997; 51: 415-462Crossref PubMed Scopus (197) Google Scholar). Successful replication of T. gondii within its PV requires a substantial increase in membrane biogenesis. Despite the apparent segregation of the PV from the host cell endocytic network, metabolites essential for the parasite are known to exchange with the intravacuolar space. Shortly after infection, the PV membrane quickly becomes physically associated with sites of host cell lipid biosynthesis, the endoplasmic reticulum and mitochondria (5Sinai A.P. Joiner K.A. Annu. Rev. Microbiol. 1997; 51: 415-462Crossref PubMed Scopus (197) Google Scholar, 6Sinai A.P. Joiner K.A. J. Cell Biol. 2001; 154: 95-108Crossref PubMed Scopus (176) Google Scholar). Therefore, these organelles might function as the donors of essential lipids to the growing parasite. Another possibility is that like Plasmodium falciparum (7Vial H.J. Ancelin M.L. Philippot J.R. Thuet M.J. Blood Cells. 1990; 16: 531-561PubMed Google Scholar), a related apicomplexan parasite, T. gondii is independent of its host regarding its lipid requirement and harbors its own lipid biosynthetic machinery. Currently there is a paucity of information about the lipid metabolism of T. gondii. A study by Charron and Sibley (8Charron A.J. Sibley L.D. J. Cell Sci. 2002; 115: 3049-3059Crossref PubMed Google Scholar) using fluorescent lipids and radioactive precursors suggested that T. gondii is capable of both autonomous phospholipid synthesis and scavenging of phosphatidylcholine (PtdCho) from the host cell, but no quantitative measurements were made. In this study, we investigated the phospholipid metabolism of the free T. gondii to gauge its capacity for membrane biogenesis independent of the host cell. We focused on the quantitative analysis of the aminoglycerophospholipid synthetic pathways that produce phosphatidylserine (PtdSer), phosphatidylethanolamine (PtdEtn), and PtdCho. In many eukaryotes the metabolism of these three lipids is intimately interconnected with the decarboxylation of PtdSer producing PtdEtn and the methylation of PtdEtn producing PtdCho (9Vance J.E. Vance D.E. Biochem. Cell Biol. 2004; 82: 113-128Crossref PubMed Scopus (263) Google Scholar). Eukaryotes also possess pathways for PtdEtn and PtdCho synthesis via the Kennedy pathways using phospho-Etn/Cho and CDP-Etn/Cho intermediates (9Vance J.E. Vance D.E. Biochem. Cell Biol. 2004; 82: 113-128Crossref PubMed Scopus (263) Google Scholar). We also investigated whether the ability of the parasite to autonomously synthesize phospholipid rendered it uniquely susceptible to modifiers of phospholipid metabolism. We specifically focused upon Etn(Me)2, which is known to alter the phospholipid composition of eukaryotic cells (10Schroeder F. Perlmutter J.F. Glaser M. Vagelos P.R. J. Biol. Chem. PubMed Google Scholar, C. M. S. J. Biochem. PubMed Scopus Google Scholar). findings reveal that the parasite a capacity for independent phospholipid synthesis and that its PtdCho metabolism is by Etn(Me)2 to a of medium and and were from The and were from The and were from and were from and was from The was from lipids were from and for thin layer were from and respectively. of Etn(Me)2 were a of in and were to the for Cell and foreskin from were in medium supplemented with 2 mm and and in a were by a and host cells were used to the T. gondii of the were in by in The parasites were in a and used for a of host invasion the of infection in the the from were and by three with phosphate-buffered The parasites were used after In the of these we the of parasites on A.P. Joiner K.A. J. Cell Biol. 2000; PubMed Scopus Google Scholar) with by and We no the and used the and for the in this of T. gondii of T. gondii was in for with parasites were with in of The intracellular medium mm mm mm mm mm and The medium mm mm in of mm and The of and was and to a of mm with mm to the The was by of of and and The of the was used for the of phospholipid. and of S. PubMed Scopus Google Scholar), parasites were in of by the of 2 of of and 2 of with The was from the and the was with from the parasites were three times with of The lipids was and in of were and by on in were also by on in and in were by with with and to lipids were on their with of 2 gondii in for was using with The were on to The were by all and to were in for to for was as a negative in the were with of by of of and of The was three times with of The was in and the was by was by from on with 2 Kennedy J. Biol. Chem. PubMed Google Scholar). was from and by the of PtdSer The PtdSer was from the which caused of the A. J. Biol. Chem. PubMed Google Scholar). The were in with an to which was a the The parasite was in mm mm and mm The mm mm PMSF, 2 mm mm mm and of parasite The was after by the of of the using a The radioactive was a of to the for was by following the of from into PtdCho in the of PubMed Scopus Google Scholar). The cell was in mm PMSF, and mm The mm mm mm mm mm mm PMSF, mm mm mm and of parasite The was by lipid was by following the of from into PtdEtn in the of PubMed Scopus Google Scholar). The cell was as for the choline The mm mm mm mm mm PMSF, mm mm mm and of parasite The was by lipid and the was three times with of phosphatidylserine was by following PtdSer synthesis from in the of M. PubMed Scopus Google Scholar). The was in mm mm PMSF, and mm The mm mm mm mm mm PMSF, mm mm and of cell The was by lipid phosphatidylserine was by following PtdSer synthesis in the of PtdEtn, and The cell was in mm mm PMSF, and mm The mm mm mm PtdEtn, mm mm mm PMSF, mm and of the cell was and with mm The was by lipid by with of The lipid was in of and on a in The PtdSer and its PtdEtn, were by with from the and to of parasite metabolism was by the of into The cells were in and with parasites a of The cells were with 2 mm Etn(Me)2 the of infection as in the of the parasites were by the with The were to medium supplemented with in the of the were with and with for on to the was with and with of The were after for The was by of human foreskin were with in for and for thin as Joiner K.A. Biol. PubMed Scopus Google Scholar) with a The Toxoplasma into PtdSer and gondii is an obligate intracellular parasite with a in The of the parasite with a of the host cell Cell Biol. 1994; PubMed Scopus Google Scholar). We phospholipid synthesis in parasites to the capacity of the for autonomous membrane biogenesis. The PtdCho, PtdEtn, and PtdSer the of membrane lipids in we the metabolism of and that this was incorporated into the parasite lipid The lipid synthesis was for the 2 and the of The major lipids from were PtdSer and PtdEtn as by thin layer in lipids with PtdCho and of thin layer PtdCho and PtdIns, these lipids were are that are to also with of these lipids was in this gondii can to synthesize PtdSer and T. gondii of the were with in medium by lipid The lipids were on a using in The phospholipid were after with The were and the was by are for three was to PtdSer that was to PtdEtn We to of methylation of PtdEtn to PtdCho also We also that the parasite might the for PtdEtn methylation in We the with in the of mm but to PtdCho synthesis quantitative in the lipid We also this in intracellular as as medium but no in metabolism. these we that the parasite PtdSer and PtdSer but PtdEtn Toxoplasma into PtdEtn but the the metabolism of by the free parasite. As in T. gondii also acquire from its environment and it into the metabolism of also a time-dependent increase in lipid synthesis that a The major lipid was PtdEtn lipids with PtdSer, PtdCho, and were also but their are to with we for of PtdEtn to PtdCho. In of with also to produce PtdCho from these we that T. gondii can synthesize PtdEtn from and that the of phospholipid is to PtdCho. Toxoplasma into of into the lipids of T. gondii was also The T. gondii acquire from the medium and it into PtdCho The metabolism was for in medium it a for The major lipid was PtdCho, and no other lipid were were in intracellular medium we a of the of PtdCho as with of the phospholipid of the free parasite by of that PtdCho was the lipid and for about of the phospholipid. The lipids were PtdEtn PtdSer and The parasite phospholipid was from that of the host cell, in the of all lipid precursors in this study, the of metabolism the by and In the intracellular the metabolism of and was largely but that of was about that metabolism in to invasion of host The lipid precursors in the were used within the of tissue culture We using that of into The of these are in The of PtdSer, PtdEtn, and PtdCho synthesis were and for of These of phospholipid synthesis were for a cell for PtdEtn, of that for PtdSer, and of that for a cell for PtdCho. These were upon a phospholipid content of T. gondii of cells as by of lipid synthesis with T. gondii were with and in the intracellular medium for and the of the precursors into lipid was by lipid and are for three the for with the in of T. we also the of in phospholipid in from parasites As from the and the of the Kennedy pathways for PtdEtn and PtdCho synthesis D.E. of and Scholar) were in from the and in the of The was more than the of as in PtdSer was using for the exchange and the The exchange was and of with The of PtdEtn in the as a of the the for PtdSer synthesis was using for the We were to demonstrate of PtdSer synthesis upon the of The PtdSer of was than that of the other lipid synthetic The of the parasite PtdSer was also about than that in from other eukaryotes J. J. Biol. Chem. 1993; PubMed Google Scholar) and mammalian cells M. J. Biol. Chem. PubMed Google Scholar). These data the and the Kennedy pathways for PtdEtn and PtdCho the exchange for PtdSer and the PtdSer for PtdEtn synthesis as in T. gondii of in aminoglycerophospholipid synthesis in T. are of three phosphatidylserine are of three in a The Etn(Me)2 T. gondii of PtdCho and its as a major lipid in T. gondii an to the membrane biogenesis of the parasite. We the effect of a choline analog, Etn(Me)2, on the intracellular replication of T. gondii. with Etn(Me)2 in mammalian cells it was an choline that was (10Schroeder F. Perlmutter J.F. Glaser M. Vagelos P.R. J. Biol. Chem. PubMed Google Scholar, C. M. S. J. Biochem. PubMed Scopus Google Scholar). the of Etn(Me)2 in tissue culture medium caused a marked inhibition of parasite replication as in In contrast, the host cells and to the choline We parasite replication by the of parasites after of culture following infection of a of this infection parasites host cell upon lysis after The parasite with the of Etn(Me)2, and 2 mm the was by in parasite and mm Etn(Me)2, but these also host cell growth. Therefore, we used 2 mm Etn(Me)2 to on parasite metabolism. We to the for the of Etn(Me)2 upon parasite cells were in Etn(Me)2 times from infection to after infection, and the of these were The in 7 reveal that the Etn(Me)2 remained parasite replication for to after infection of the after parasite infection of the choline was a of parasite We also that the effect of Etn(Me)2 was that of the the parasites to to after a these we that Etn(Me)2 is but We in which we the of to Etn(Me)2 after infection and that the no effect upon invasion infection but as the parasite to within the host cell The metabolism of the parasites was also by following the of into as in The cells in the of Etn(Me)2 incorporated into In contrast, the cells incorporated of into with the host of host cells with 2 mm Etn(Me)2 for the of by as in in synthesis to the the parasites remained but to as in the of Etn(Me)2 by and that Etn(Me)2 is by tissue culture cells and incorporated into (10Schroeder F. Perlmutter J.F. Glaser M. Vagelos P.R. J. Biol. Chem. PubMed Google Scholar, C. M. S. J. Biochem. PubMed Scopus Google Scholar). As in the host cells used in these Etn(Me)2 into and the lipid to as much as of phospholipid after The increase in was paralleled by a decrease in PtdCho. were no in other and the morphology of the cells by We the of Etn(Me)2 upon phospholipid metabolism of T. gondii within the host cell and after from the host cell. study the metabolism within the host cell, we for in the of mm Etn(Me)2, which in a but of parasites for phospholipid analysis The of these are in and demonstrate that T. gondii to of its as and the PtdCho content from to of phospholipid. these we 2 mm Etn(Me)2, the of the in the parasite is to of the of with 2 mm Etn(Me)2 that after of the lipid about of the phospholipid of the host cell. the intracellular parasite the ability to to more than than the host The of by the parasite a of synthesis of the lipid by the of the lipid from the host cell. the in content the host cell and the parasite it that T. gondii the lipid we to this parasites were in intracellular medium and lipid precursors in to 2 mm the lipids were from the parasites and by thin layer and The in demonstrate that the parasite synthesize PtdCho, PtdIns, PtdOH, and of 2 mm Etn(Me)2 in the medium to the synthesis of to as as of the phospholipid these we that the free parasite the and to synthesize we that the and PtdEtn of the lipids of that can in We the of this In we also the of Etn(Me)2 upon the of into phospholipid by the free parasite. The of these in reveal that Etn(Me)2 was a of choline and metabolism to the of Etn(Me)2 the parasites remained to synthesize PtdCho of the for The of Etn(Me)2 on metabolism were selective there was no effect upon into and into lipid Etn(Me)2 The of parasite growth in host cells was the and with intracellular T. gondii by which is a specialized of within the of the cell. of parasites with mm Etn(Me)2 in a decrease in parasite the PV 2 parasites in cells In to parasites parasites were also within the a of a in the of more parasite a of parasite growth after three of might as a of PtdCho for membrane biogenesis. 2 mm Etn(Me)2, the PV an of 2 2 parasites with and and parasite were also is of a disruption of parasite as a of the in parasite membranes. with membrane were in the parasite of the of membrane lipid In contrast, the host cells demonstrate abnormalities upon Etn(Me)2 The parasitophorous membrane of T. gondii is intimately associated with host cell mitochondria and endoplasmic reticulum (5Sinai A.P. Joiner K.A. Annu. Rev. Microbiol. 1997; 51: 415-462Crossref PubMed Scopus (197) Google Scholar, 6Sinai A.P. Joiner K.A. J. Cell Biol. 2001; 154: 95-108Crossref PubMed Scopus (176) Google Scholar). host organelle to a in lipid and membrane scavenging from these organelles by intravacuolar both host mitochondria and endoplasmic reticulum were associated with the parasitophorous membrane to the in and cells these data we that Etn(Me)2 alters parasite phospholipid synthesis and replication but also structural abnormalities in the of T. gondii. T. gondii is an important human capable of causing disease in and immunocompromised individuals (1Tenter A.M. Heckeroth A.R. Weiss L.M. Int. J. Parasitol. 2000; 30: 1217-1258Crossref PubMed Scopus (2366) Google Scholar, B.J. Hafner R. Korzun A.H. Leport C. Antoniskis D. Bosler E.M. Bourland D.D. II I Uttamchandani R. Fuhrer J. Jacobson J. Morlat P. Vilde J-L. Remington J.S. N. Engl. J. Med. 1993; 329: 995-1000Crossref PubMed Scopus (366) Google Scholar, S.Y. Remington J.S. Clin. Infect. Dis. 1994; 18: 853-862Crossref PubMed Scopus (316) Google Scholar). Currently there is a paucity of information about the lipid metabolism of the parasite. In this we of the of aminoglycerophospholipid metabolism in the and a of the parasite to of PtdCho metabolism. the autonomous ability of the parasite to synthesize PtdSer, PtdEtn, and PtdCho. of lipid we that free parasites synthetic capacity to produce all of the PtdEtn and of the PtdSer for a cell The free parasites synthesize of the for a cell it is whether PtdCho synthesis is in to host cell invasion whether of PtdCho are from the host cell. Charron and Sibley (8Charron A.J. Sibley L.D. J. Cell Sci. 2002; 115: 3049-3059Crossref PubMed Google Scholar) suggested that the parasite can acquire PtdCho from the host cell. with and intracellular that PtdCho synthesis is in the environment that the parasite upon invasion of the host cell. is that host cell increase PtdCho synthesis. the and the in measurements of demonstrate that the parasite is capable of autonomous aminoglycerophospholipid synthesis the host cell. These demonstrate the of the Kennedy pathways for PtdEtn and PtdCho the exchange for PtdSer and the PtdSer as an for PtdEtn synthesis. the of the in parasites with precursors by measurements the quantitative for lipids for replication and the synthetic These of of the parasites the from the intracellular to the of the The of of from to of the PtdSer was the In with other the in cell was than the for and mammalian These of that PtdSer a in the of the parasite. of the and with the and information from T. gondii information about the ability of the parasite to synthesize lipids The T. gondii of the for in with to of the Kennedy for the synthesis of PtdEtn and PtdCho choline and and and and for PtdSer and and PtdSer and are also The data for T. gondii also to PtdSer and but we were to this analysis to whether this is other of the parasite important into phospholipid metabolism that were for this apicomplexan parasite. T. gondii PtdSer and a substantial of the phospholipid to of PtdSer decarboxylation is with that in host cells but is to that of the related parasite P. T. gondii no of PtdCho from and precursors (7Vial H.J. Ancelin M.L. Philippot J.R. Thuet M.J. Blood Cells. 1990; 16: 531-561PubMed Google Scholar, N. Ancelin M.L. H.J. Biochem. J. 1997; PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. 2004; PubMed Scopus Google Scholar). is for PtdEtn from free as as that from These findings demonstrate that T. gondii is a choline PtdCho The of T. gondii on an of choline for PtdCho synthesis the possibility that this for upon its replication within host We this by cells with Etn(Me)2 and the upon parasite growth and Despite the findings that Etn(Me)2 as a choline and was to mammalian cells (10Schroeder F. Perlmutter J.F. Glaser M. Vagelos P.R. J. Biol. Chem. PubMed Google Scholar), it the growth and of T. gondii a 2 mm the Etn(Me)2 the of parasitophorous in host cells and it also dramatically the of parasites the parasite cell was the of infection, and the of parasites of host cells was by of The of of metabolism in the parasite was also with the that parasite growth is by 2 mm In this effect upon parasite growth for the of host cell We that the of Etn(Me)2 are of this from to of the parasite a of effect of Etn(Me)2 is the of its The Etn(Me)2 was the of infection to after after infection, the Etn(Me)2 inhibited parasite production the by These findings are with a in lipid metabolism that parasite growth and A of choline and for their ability to alter the growth of apicomplexan P. falciparum M. J. M. T. Ancelin M.L. J. Med. Chem. 1997; PubMed Scopus Google Scholar, M.L. M. J. D. M. T. P. H.J. PubMed Google Scholar). The major effect of these to of PtdCho but the and sites of of the are Etn(Me)2 also in these but the of of phospholipid metabolism M. J. M. T. Ancelin M.L. J. Med. Chem. 1997; PubMed Scopus Google Scholar, M.L. M. J. D. M. T. P. H.J. PubMed Google Scholar). In the study we that the of in with the in PtdCho synthesis by T. gondii is to the growth of the parasite within the host cell. The that Etn(Me)2 alters phospholipid metabolism from In we used of Etn(Me)2 the for parasite we the effect of the upon the parasite phospholipid composition within the host cell. that the parasites of PtdEtn(Me)2, it the major phospholipid within the cell. The of in the parasite the within the host cell the autonomous synthesis of by the parasite. In a we the synthesis of by free parasites using Etn(Me)2 and The demonstrate that the parasite can synthesize of the host cell. In we also that Etn(Me)2 for the of into PtdCho. the synthesis of within the parasite with a in PtdCho synthesis. As the of synthesis of PtdCho for the free parasite was than that for a cell the possibility that PtdCho from the host cell after the parasite to PtdCho from host cells to the of Etn(Me)2 PtdEtn These findings that the of PtdCho from the host cell by T. gondii is to a PtdCho synthesis is The of also it that the parasite is capable of phospholipid is as an in the of PtdEtn to PtdCho. capable of phospholipid methylation to PtdCho (9Vance J.E. Vance D.E. Biochem. Cell Biol. 2004; 82: 113-128Crossref PubMed Scopus (263) Google Scholar). of the parasites by that Etn(Me)2 dramatically their membrane membrane and were for to the choline The that the are in their membrane biogenesis. whether these as a of of PtdCho the of in both in In data an of synthesis in T. gondii of autonomous synthesis of PtdSer, PtdEtn, and PtdCho. The PtdEtn can from PtdSer as as The autonomous synthesis of PtdEtn for cell whereas that of PtdCho of that for cell The of PtdCho synthesis that the intracellular environment and to by within the host cell. The choline Etn(Me)2 is incorporated into by the parasite, and replication within the host cell it becomes the major phospholipid of the parasite. The selective disruption of PtdCho synthesis with dramatically parasite replication and alters membrane and of PtdCho synthesis in T. gondii a for the parasite growth in human cells and for of on the