Growth Phase Regulation of the Main Folate Transporter of Leishmania infantum and Its Role in Methotrexate Resistance

The protozoan parasite Leishmania relies on the uptake of folate and pterin from the environment to meet its nutritional requirements. We show here that a novel gene (folate transporter 1 (FT1)) deleted in a Leishmania infantum methotrexate-resistant mutant corresponds to the main folate transporter (Km, 410 nm). FT1 was established as the main folate transporter by both gene transfection and by targeted gene deletion. Modulation of the expression of FT1 by these manipulations altered the susceptibility of Leishmania cells to methotrexate. Folate transport was stage-regulated with higher activity in the logarithmic phase and less in the stationary phase. FT1 fused to green fluorescent protein led to the observation that FT1 was located in the plasma membrane in the logarithmic phase but was retargeted to an intracellular organelle followed by a degradation of the protein in stationary phase. Leishmania has several folate transporters with different characteristics, and the growth stage-related activity of at least one transporter is regulated post-translationally. The protozoan parasite Leishmania relies on the uptake of folate and pterin from the environment to meet its nutritional requirements. We show here that a novel gene (folate transporter 1 (FT1)) deleted in a Leishmania infantum methotrexate-resistant mutant corresponds to the main folate transporter (Km, 410 nm). FT1 was established as the main folate transporter by both gene transfection and by targeted gene deletion. Modulation of the expression of FT1 by these manipulations altered the susceptibility of Leishmania cells to methotrexate. Folate transport was stage-regulated with higher activity in the logarithmic phase and less in the stationary phase. FT1 fused to green fluorescent protein led to the observation that FT1 was located in the plasma membrane in the logarithmic phase but was retargeted to an intracellular organelle followed by a degradation of the protein in stationary phase. Leishmania has several folate transporters with different characteristics, and the growth stage-related activity of at least one transporter is regulated post-translationally. Leishmaniasis is caused by protozoan parasites of the genus Leishmania and can result in a variety of clinical symptoms with visceral infections that are usually fatal if left untreated (1Herwaldt B.L. Lancet. 1999; 354: 1191-1199Abstract Full Text Full Text PDF PubMed Scopus (1356) Google Scholar). Even today, pentavalent antimonial agents are the mainstay for the control of this disease. However, resistance to this class of drugs is now prevalent in several endemic areas (2Sundar S. More D.K. Singh M.K. Singh V.P. Sharma S. Makharia A. Kumar P.C. Murray H.W. Clin. Infect. Dis. 2000; 31: 1104-1107Crossref PubMed Scopus (531) Google Scholar) demonstrating the urgent need for novel effective treatment alternatives. As a result of the effort to discover new drugs, miltefosine, an inhibitor of alkyl phospholipid metabolism, has recently been approved for the treatment of visceral leishmaniasis in India (3Sundar S. Jha T.K. Thakur C.P. Engel J. Sindermann H. Fischer C. Junge K. Bryceson A. Berman J. N. Engl. J. Med. 2002; 347: 1739-1746Crossref PubMed Scopus (614) Google Scholar). Unfortunately the ease with which miltefosine-resistant Leishmania mutants can be generated in vitro suggests a strong potential for the appearance of such mutants in the field (4Perez-Victoria F.J. Gamarro F. Ouellette M. Castanys S. J. Biol. Chem. 2003; 278: 49965-49971Abstract Full Text Full Text PDF PubMed Scopus (188) Google Scholar); thus there is still a need for the development of effective new therapies against this parasite. The folate biosynthesis pathway has been exploited extensively for the development of a variety of drugs. Folates are made of a pterin moiety conjugated to para-aminobenzoic acid and glutamic acid. Reduced folates are key cofactors in the biosynthesis of thymidylate, and inhibitors of this pathway act primarily at the level of dihydrofolate reductase, the enzyme responsible for supplying the cell with reduced folates (for reviews, see Refs. 5Schweitzer B.I. Dicker A.P. Bertino J.R. FASEB J. 1990; 4: 2441-2452Crossref PubMed Scopus (300) Google Scholar and 6Zhao R. Goldman I.D. Oncogene. 2003; 22: 7431-7457Crossref PubMed Scopus (217) Google Scholar). Antifolates are widely used in chemotherapy but have not been successful yet against infections caused by Leishmania. Nevertheless many distinct features in the folate metabolism of this organism have been identified, some of which could prove to be useful therapeutic targets (7Nare B. Luba J. Hardy L.W. Beverley S. Parasitology. 1997; 114: S101-S110Crossref PubMed Google Scholar, 8Ouellette M. Drummelsmith J. El-Fadili A. Kundig C. Richard D. Roy G. Int. J. Parasitol. 2002; 32: 385-398Crossref PubMed Scopus (75) Google Scholar). A number of lead antifolate molecules were indeed shown to be active against Leishmania (for a review, see Ref. 9Gilbert I.H. Biochim. Biophys. Acta. 2002; 1587: 249-257Crossref PubMed Scopus (96) Google Scholar). Our understanding of pterin and folate metabolism and transport in Leishmania is due in large part to studies of resistance mechanisms to the model antifolate drug methotrexate (MTX) 1The abbreviations used are: MTX, methotrexate; BT1, biopterin transporter 1; FT1, folate transporter 1; FT3, folate transporter 3; FT5, folate transporter 5; GFP, green fluorescent protein; EGFP, enhanced GFP; HA, hemagglutinin; Li, L. infantum; HYG, hygromycin phosphotransferase; NEO, neomycin phosphotransferase; DKO, double knockout; SKO, single knock-out; PGPD, p-glycoprotein D. 1The abbreviations used are: MTX, methotrexate; BT1, biopterin transporter 1; FT1, folate transporter 1; FT3, folate transporter 3; FT5, folate transporter 5; GFP, green fluorescent protein; EGFP, enhanced GFP; HA, hemagglutinin; Li, L. infantum; HYG, hygromycin phosphotransferase; NEO, neomycin phosphotransferase; DKO, double knockout; SKO, single knock-out; PGPD, p-glycoprotein D. (for reviews, see Refs. 7Nare B. Luba J. Hardy L.W. Beverley S. Parasitology. 1997; 114: S101-S110Crossref PubMed Google Scholar and 8Ouellette M. Drummelsmith J. El-Fadili A. Kundig C. Richard D. Roy G. Int. J. Parasitol. 2002; 32: 385-398Crossref PubMed Scopus (75) Google Scholar). Resistance to MTX in Leishmania can be conferred by several genes but is also usually correlated with a reduced accumulation of the drug (10Papadopoulou B. Roy G. Ouellette M. Nucleic Acids Res. 1993; 21: 4305-4312Crossref PubMed Scopus (62) Google Scholar, 11Ellenberger T.E. Beverley S.M. J. Biol. Chem. 1987; 262: 13501-13506Abstract Full Text PDF PubMed Google Scholar, 12Kaur K. Coons T. Emmett K. Ullman B. J. Biol. Chem. 1988; 263: 7020-7028Abstract Full Text PDF PubMed Google Scholar). This reduced uptake of MTX is paralleled by a marked decrease in folate uptake, suggesting that the expression of a common folate/MTX transporter is strongly down-regulated in some MTX-resistant Leishmania. Since Leishmania is a folate auxotroph, mutants with markedly reduced folate uptake must compensate for this decrease so the parasite can meet its folate requirements. In Leishmania tarentolae, the mechanism of compensation involves the overexpression of the biopterin transporter 1 (BT1), which transports folates but not MTX to meet the folate requirements of the cell (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar). BT1 is a biopterin transporter (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar, 14Lemley C. Yan S. Dole V.S. Madhubala R. Cunningham M.L. Beverley S.M. Myler P.J. Stuart K.D. Mol. Biochem. Parasitol. 1999; 104: 93-105Crossref PubMed Scopus (62) Google Scholar) that is part of a family of transmembrane proteins. Fourteen putative proteins belonging to this family are part of the Leishmania genome (www.genedb.org). This family has members in a variety of organisms, including the related parasite Trypanosoma brucei as well as the plant Arabidopsis thaliana and the cyanobacteria Synechocystis and Synechococcus. A second member of this family in Leishmania, the folate transporter 5 (FT5), was recently investigated and shown to be a very high affinity and low capacity folate/MTX transporter (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). However, FT5 does not correspond to the main Leishmania folate transporter. Folate transport in Leishmania is known to be regulated with the growth stage of the parasite with high activity in the logarithmic stage of the parasite and residual activity in the stationary phase (16Ellenberger T.E. Beverley S.M. J. Biol. Chem. 1987; 262: 10053-10058Abstract Full Text PDF PubMed Google Scholar, 17Cunningham M.L. Beverley S.M. Mol. Biochem. Parasitol. 2001; PubMed Scopus Google Scholar). studies of the folate transporter 1 a transporter belonging to the BT1 and that corresponds to the high affinity folate/MTX transporter of Leishmania Modulation of the expression of FT1 antifolate The FT1 protein was located in the plasma membrane in the logarithmic growth phase of the but the protein was retargeted the parasite the stationary growth phase. Leishmania Leishmania infantum and the L. cells and the mutant cell have been (10Papadopoulou B. Roy G. Ouellette M. Nucleic Acids Res. 1993; 21: 4305-4312Crossref PubMed Scopus (62) Google Scholar, D. Roy G. Papadopoulou B. Ouellette M. 2001; PubMed Scopus Google Scholar). L. infantum and L. cells were in with and and 5 Leishmania were by as B. Roy G. Ouellette M. EMBO J. PubMed Scopus Google Scholar). In this also the FT1 gene in and generated an L. infantum with one FT1 and with FT1 In the cell also an of the FT1 was was J. T. A Scholar). The L. folate transporter Ref. D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar) and the L. infantum FT1 were by The used were and for and and for 1 and The and in 1 and are of FT1 gene was from a from a L. infantum with a L. The gene was by with 1 and with and and the Leishmania expression A. Kundig C. Ouellette M. Mol. Biochem. Parasitol. 2002; PubMed Scopus Google Scholar). The was made by the protein which resistance to the drug the as The was with and the FT1 gene to The was by of the FT1 gene 1 and see of the by and and in The enhanced gene D. Richard D. R. Haimeur A. Papadopoulou B. Ouellette M. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) was by with and with and and with This was in A control was made by an of the protein D. Ouellette M. Mol. Biochem. Parasitol. PubMed Scopus Google Scholar) with the of was deleted by the of the gene by an the The gene was by with one of the a to the of the The was the The was in the expression B. Roy G. Ouellette M. EMBO J. PubMed Scopus Google Scholar). of an FT1 the FT1 of the gene were by A was and The was with and and and B. Roy G. Ouellette M. Mol. Biochem. Parasitol. PubMed Scopus (75) Google Scholar). the a was 5 and The was with and and with the FT1 The were and in a neomycin and a hygromycin The was used to one FT1 by The was used to the second FT1 in the and the with a the were to the of the was on an of the was the and The here has been in the the number were as (10Papadopoulou B. Roy G. Ouellette M. Nucleic Acids Res. 1993; 21: 4305-4312Crossref PubMed Scopus (62) Google Scholar). and were from studies were of to 1 to the affinity The of was with Leishmania cell folate and MTX the uptake of cells on was were with and on with were with an on an with an of the was a and were for green a and of were and protein and with were D. A Scholar). of of the BT1 in L. cells for MTX resistance a in the transport of MTX and folate (10Papadopoulou B. Roy G. Ouellette M. Nucleic Acids Res. 1993; 21: 4305-4312Crossref PubMed Scopus (62) Google Scholar, 11Ellenberger T.E. Beverley S.M. J. Biol. Chem. 1987; 262: 13501-13506Abstract Full Text PDF PubMed Google Scholar, 12Kaur K. Coons T. Emmett K. Ullman B. J. Biol. Chem. 1988; 263: 7020-7028Abstract Full Text PDF PubMed Google Scholar). The proteins responsible for the transport of and folates in Leishmania are to be known and correspond to a novel family of membrane proteins known as the BT1 family BT1 is a high affinity (Km, biopterin transporter (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar, 14Lemley C. Yan S. Dole V.S. Madhubala R. Cunningham M.L. Beverley S.M. Myler P.J. Stuart K.D. Mol. Biochem. Parasitol. 1999; 104: 93-105Crossref PubMed Scopus (62) Google Scholar). The L. genome suggests the of proteins part of the BT1 of these genes can be deleted in cells with reduced folate/MTX transport (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar, A. Kundig C. Roy G. Ouellette M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the folate/MTX transporter generated L. infantum MTX-resistant of these a in MTX accumulation that was paralleled by a decrease in acid accumulation of members of the BT1 family correlated with a in the of Leishmania cells to a from the L. This is known to several members of the BT1 gene family (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). As several were the some of these one but at least of these were deleted in to gene a new of was in the one of the deleted could correspond to the main folate a L. infantum the from the were and of a that to be deleted in the mutant The of this and on the an of in a protein of The protein by this is and to the L. and FT5, and to the Leishmania BT1 of these proteins are in the parasites Leishmania T. and Trypanosoma in the parasites and in A. and in the cyanobacteria Synechocystis and Synechococcus. In the now Leishmania genome a of putative transporters have been on and and in Leishmania a of putative transporter genes to were to the gene and not that the number is related to a of L. with the with FT1 number and thus the FT1 for the L. infantum This family of putative transporters is to putative transmembrane but is not related to of transport including proteins known to transport folates in acid of the L. infantum folate transporter The of the number was with the L. biopterin transporter BT1 and the L. high affinity folate transporter FT5 and putative transporter are in acid are FT1 is and to FT3, FT5, and BT1, FT1 the L. infantum Folate L. infantum gene FT1 was an expression and in the L. mutant in which folate and MTX uptake are (10Papadopoulou B. Roy G. Ouellette M. Nucleic Acids Res. 1993; 21: 4305-4312Crossref PubMed Scopus (62) Google Scholar, D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). and acid uptake were for this and with the accumulation of folate MTX was in the mutant cells the an in both acid and MTX transport in the The level of accumulation in the with in the L. infantum cells suggesting that FT1 be the folate transporter. This was by of the of this FT1 transporter for folate and methotrexate as a double the was to be to the in Leishmania cells of folate transport in L. of with a of from to of with a of from to in a new prove that FT1 is the main folate transporter of L. infantum generated an FT1 mutant by the of FT1 by expression The of and of of the FT1 gene for The was in L. and in the of were by In an FT1 a Since FT1 is part of a gene were also of the in the of an lead to a new of to the is at least one folate transporter FT1 on this This is by one Since Leishmania is a one FT1 to be The was thus the single in the of both and hygromycin were by The of the also led to the of a thus an to the FT1 The of the were by with and The was in both the FT1 single and double mutant cells and the as to the from the mutant The of the was by and with a of the FT1 gene but the As were in cells 1 and in a single the In the double and of the were 5 and that both the The of both and in the FT1 gene that there are of the However, a of the of an FT1 still to an FT1 in the The of the was in the suggesting that indeed FT1 was and that genes with FT1 as was in the FT5 mutant (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). The of the mutant indeed that were with an FT1 mutant decrease in the transport of acid and MTX was in the mutant A and The mutant still of transport for both This residual transport could be due to the of FT5 in L. (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar) to members of the BT1 that this in acid and MTX transport was due to the of FT1, the mutant with with this a in the level of transport of both to A and that the decrease in transport was indeed due to of FT1 and in mutant is to MTX and is with a marked in the uptake of the drug from the of several genes belonging to the BT1 family (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). of in this mutant the transport of both folate and MTX and the FT1 was to be to MTX the to the level of cells of members of the BT1 family is correlated with MTX resistance D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar and thus an FT1 mutant be to to the The mutant an higher the the an in MTX resistance of an of FT1 in the mutant the in cells FT1 a in the of the FT1 generated an FT1 protein fused to at its The was transfection in the mutant led to of folate transport to of the protein and of the in the logarithmic phase of plasma membrane of the protein Folate uptake in L. is on growth phase with activity in the logarithmic phase and residual activity in the stationary phase (16Ellenberger T.E. Beverley S.M. J. Biol. Chem. 1987; 262: 10053-10058Abstract Full Text PDF PubMed Google Scholar, 17Cunningham M.L. Beverley S.M. Mol. Biochem. Parasitol. 2001; PubMed Scopus Google Scholar). of folate uptake in L. cells a growth phase the of was in cells with accumulation the parasites from logarithmic to stationary phase of FT1 the growth phase of the parasite. of and 5 and are shown at and of growth are shown at and of growth of the protein the growth phase of the parasite were by an protein from a is shown at and of growth protein from a is shown at and of growth protein from a is shown at and of growth the 1 cells were in 5 of and were growth proteins from parasites were in were the Our to its the growth The protein was to the plasma membrane logarithmic phase folate uptake was higher and As the parasites logarithmic phase the transporter could still be at the a of the to have a distinct L. the stationary phase the accumulation of folate was reduced by with the logarithmic phase The of the protein in stationary phase parasites to the plasma membrane and to have been stationary phase the distinct one the and one to the of the parasite not the growth phase of the the of a with the transporter D. Ouellette M. Mol. Biochem. Parasitol. PubMed Scopus Google Scholar). was to to an intracellular organelle the of the in of the protein logarithmic and stationary of the parasite 5 and the of in its protein of parasites at different of growth with an The of the protein is and of proteins from logarithmic phase cells protein of and The to the 1 and be degradation that in the of the to the protein in from cells in stationary phase and The decrease in was with an in the of a at and This could be due to a degradation of the FT1 protein to the of a GFP, a that has been with Leishmania proteins Mol. Biol. 2001; PubMed Scopus Google Scholar, Mol. PubMed Scopus Google Scholar). this the as the protein in Leishmania cells of from a and a in both logarithmic and stationary phase protein degradation are with folate transport in Leishmania growth by of the FT1 protein from the plasma membrane to an intracellular Leishmania is a pterin and folate and to these from the The proteins in the of these molecules are BT1 is a biopterin transporter (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar, 14Lemley C. Yan S. Dole V.S. Madhubala R. Cunningham M.L. Beverley S.M. Myler P.J. Stuart K.D. Mol. Biochem. Parasitol. 1999; 104: 93-105Crossref PubMed Scopus (62) Google Scholar) gene is in field suggesting that biopterin uptake is for Leishmania of BT1 to including MTX and reduced in (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar, M.L. Beverley S.M. 2001; PubMed Scopus Google Scholar, G. Kundig C. M. Papadopoulou B. Ouellette M. Parasitol. 2001; PubMed Scopus Google Scholar, B. Roy G. M. Kundig C. C. Singh M. Ouellette M. Infect. 2002; PubMed Scopus Google Scholar). FT5, a high affinity low capacity folate/MTX transporter. The FT5 gene is part of a large some members of which are deleted in MTX-resistant In these transport of both acid and MTX is The Leishmania genome that could be part of the BT1 The of proteins in this family are but as FT5 is not the folate transporter (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google this suggests that member of the BT1 family Leishmania for MTX resistance and markedly MTX transport have several members of the family deleted D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar and A. Kundig C. Roy G. Ouellette M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar and We were to and FT1 from L. infantum by for genes with of the as the deleted in the FT1 to a high affinity and high capacity folate transporter and with to L. infantum FT1 activity for of folate transport in Leishmania The transport was due to FT5 BT1 family Leishmania and and its the parasite with to of the high folate in the Leishmania the parasite could have a high capacity transporter In the is the higher affinity transporter FT5 a BT1 could have the to transport different of genes are expression at the parasite M.L. Beverley S.M. Mol. Biochem. Parasitol. 2001; PubMed Scopus Google Scholar). Folate transport and the proteins have been extensively in (for a review, see Ref. Goldman 2003; PubMed Scopus Google Scholar). Folate transport have been in D. R. R. Biol. PubMed Scopus Google Scholar) and in J. Biol. Chem. 1987; 262: Full Text PDF PubMed Google Scholar, B. J. Biol. Chem. Full Text PDF PubMed Google but the gene responsible for these have not yet been and on FT5 and FT1 the of folate The here that FT1 is an MTX resistance of this gene the MTX-resistant mutant L. this resistance by MTX uptake of FT1 led to MTX resistance these were not as as This can be one transporter gene is usually deleted in mutant cells D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar and and several resistance mechanisms in the cell (13Kundig C. Haimeur A. Legare D. Papadopoulou B. Ouellette M. EMBO J. 1999; 18: 2342-2351Crossref PubMed Scopus (87) Google Scholar, A. Kundig C. Roy G. Ouellette M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, C. N. C. N. A. R. G. Richard D. N. Papadopoulou B. J. Legare D. Ouellette M. Nucleic Acids Res. 2003; 31: PubMed Scopus Google Scholar). in the transport of MTX was higher in the mutant in the L. infantum mutant and This result suggests that at least one gene FT1 must be deleted to MTX transport activity as in the mutant of FT5 does not lead to MTX resistance cells are in (15Richard D. Kundig C. Ouellette M. J. Biol. Chem. 2002; 277: 29460-29467Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). This FT1 from Folates are in of the for an activity that is primarily in logarithmic phase parasites Beverley S.M. S. A. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). This folate transport activity is regulated with the growth phase of the parasite T.E. Beverley S.M. J. Biol. Chem. 1987; 262: 13501-13506Abstract Full Text PDF PubMed Google Scholar, 17Cunningham M.L. Beverley S.M. Mol. Biochem. Parasitol. 2001; PubMed Scopus Google Scholar). a were to show that the in folate transport the from logarithmic to stationary phase was due to a of the protein that in its degradation A and least Leishmania the and the resistance protein to be growth stage-regulated with to the followed by degradation Mol. Biol. 2001; PubMed Scopus Google Scholar, Mol. PubMed Scopus Google Scholar); FT1 is the of a plasma membrane protein in Leishmania this of in protein could thus level and activity of different of proteins in Leishmania. on its the organelle to which the protein is targeted stationary phase could be the The has been to be a protein degradation A. Engel 2001; PubMed Scopus Google Scholar). In cells a number of membrane proteins and are and in a number of intracellular and proteins to be key of membrane protein transport and and degradation (for a review, see Ref. L. R. Biol. 2003; PubMed Scopus Google Scholar). are to the of the folate transporter FT1 by a In a novel gene in Leishmania that corresponds to the high affinity folate transporter. We that the of folate transport at least in of a growth degradation of the FT1 be to this of to members of the BT1 family and to Leishmania proteins.

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