Transport of Sulfonium Compounds

It has been reported that GAP1 and AGP2 catalyze the uptake of polyamines together with amino acids in Saccharomyces cerevisiae. We have looked for polyamine-preferential uptake proteins in S. cerevisiae. DUR3 catalyzed the uptake of polyamines together with urea, and SAM3 was found to catalyze the uptake of polyamines together with S-adenosylmethionine, glutamic acid, and lysine. Polyamine uptake was greatly decreased in both DUR3-and SAM3-deficient cells. The K m values for putrescine and spermidine of DUR3 were 479 and 21.2 M, respectively, and those of SAM3 were 433 and 20.7 M, respectively. Polyamine stimulation of cell growth of a polyamine requiring mutant, which is deficient in ornithine decarboxylase, was not influenced by the disruption of GAP1 and AGP2, but it was diminished by the disruption of DUR3 and SAM3. Furthermore, the polyamine stimulation of cell growth of a polyamine-requiring mutant was completely inhibited by the disruption of both DUR3 and SAM3. The results indicate that DUR3 and SAM3 are major polyamine uptake proteins in yeast. We previously reported that polyamine transport protein kinase 2 regulates polyamine transport. It was found that DUR3 (but not SAM3) was activated by phosphorylation of Thr 250 , Ser 251 , and Thr 684 by polyamine transport protein kinase 2.Polyamines (putrescine, spermidine, and spermine) in cells, which are essential for cell growth, are regulated by biosynthesis, degradation, and transport (1-4). With regard to polyamine transport, the properties of four polyamine transport systems were characterized in Escherichia coli (5-8). They include spermidine-preferential and putrescine-specific uptake systems as well as PotE (involved in the excretion of putrescine by a putrescine-ornithine antiporter activity) and CadB (involved in the excretion of cadaverine by a cadaverine-lysine antiporter activity). The former two transport systems function at neutral pH (2), whereas the latter two transport systems at acidic pH (9). In Saccharomyces cerevisiae, we identified four genes that encode polyamine excretion proteins TPO1-TPO4, mainly located on the plasma membrane (10 -12). We also found that UGA4 (located on vacuoles) can catalyze the uptake of ␥-aminobutyric acid and putrescine (13), and TPO5 (located on Golgi or post-Golgi secretory vesicles) can catalyze the excretion of polyamines (14). Furthermore, we reported that GAP1, located on the plasma membrane, can catalyze the uptake of putrescine and spermidine together with the uptake of amino acids (15). Although it has been reported that AGP2 can selectively catalyze the uptake of spermidine (16), there is also a report that AGP2 functions as an amino acid permease (17). In this study, we looked for proteins that can preferentially catalyze the uptake of polyamines in S. cerevisiae. We found that DUR3 can catalyze the uptake of polyamines together with urea, and SAM3 (which belongs to the family of amino acid polyamine-organocation transporters (18)) can catalyze the uptake of putrescine and spermidine together wit...

Section: Resultsmentioning

confidence: 70%

Section: Methodsmentioning

confidence: 99%

Polyamine Uptake by DUR3 and SAM3 in Saccharomyces cerevisiae

Uemura

Kashiwagi

Igarashi

2007

“…The transport of AdoMet in spheroplasts has been documented (42)(43)(44); however, information regarding the transport of AdoMet in vacuoles is lacking. Sam3p was discovered to function as a high affinity AdoMet permease that mediates transport of the amino acid across the plasma membrane (44).…”

Section: Discussionmentioning

confidence: 99%

“…AdoMet is also transported into yeast cells by a low affinity transport system that appears to be carrier-mediated facilitated diffusion (44). Although the transport of several amino acids across the vacuolar membrane has been described (45), the vacuolar transporter responsible for AdoMet uptake remains to be elucidated.…”

Section: Figmentioning

confidence: 99%

Regulation of S-Adenosylmethionine Levels in Saccharomyces cerevisiae

Chan¹,

Appling

2003

Folate derivatives, which are present in virtually every known organism and cell type, mediate one-carbon (C 1 ) transfers that play essential roles in several key cellular processes. Folate-dependent one-carbon metabolism is necessary for the syntheses of purines, thymidylate, formylmethionyl-tRNA, glycine, serine, and methionine (1, 2). Furthermore, many methylated molecules such as nucleic acids, proteins, and lipids are formed by transmethylation reactions with S-adenosylmethionine. This latter compound is synthesized indirectly by a folate-dependent pathway (Fig. 1) and is second only to ATP as the most abundantly used cofactor in metabolic reactions. In addition to serving as a methyl group donor, the propylamine group of decarboxylated S-adenosylmethionine can be used in the synthesis of spermidine from putrescine; donation of a second propylamine group results in the formation of spermine.Methylenetetrahydrofolate reductase (MTHFR) 1 participates in methionine metabolism as shown in Fig.

“…The only eukaryotic plasma membrane AdoMet transporter characterized to date is the Saccharomyces cerevisiae SAM3 protein (18) belonging to the amino acid permease superfamily. Although SAM3 transports AdoMet, it also transports polyamines with high affinity (19).…”

mentioning

confidence: 99%

High Affinity S-Adenosylmethionine Plasma Membrane Transporter of Leishmania Is a Member of the Folate Biopterin Transporter (FBT) Family

Dridi¹,

Ouameur²,

Ouellette

2010

S-Adenosylmethionine (AdoMet) is an important methyl group donor that plays a central role in many essential biochemical processes. The parasite Leishmania can both synthesize and transport AdoMet. Leishmania cells resistant to the antifolate methotrexate due to a rearrangement in folate biopterin transporter (FBT) genes were cross-resistant to sinefungin, an AdoMet analogue. FBT gene rearrangements were also observed in Leishmania major cells selected for sinefungin resistance. One of the rearranged FBT genes corresponded to the main AdoMet transporter (AdoMetT1) of Leishmania as determined by gene transfection and gene inactivation experiments. AdoMetT1 was determined to be a high affinity plasma membrane transporter expressed constitutively throughout the growth phases of the parasite. Leishmania cells selected for resistance or naturally insensitive to sinefungin had lower expression of AdoMetT1. A new function in one carbon metabolism, also a pathway of interest for chemotherapeutic interventions, is described for a novel class of membrane proteins found in diverse organisms.The parasite Leishmania is distributed globally and causes a variety of clinical symptoms ranging from self-healing cutaneous lesions to visceral infections that are usually fatal if left untreated (1, 2). Current first-line chemotherapy against leishmaniasis relies on a rather limited arsenal of drugs, including pentavalent antimonials, liposomal amphotericin B, or miltefosine (2). These drugs are associated with side effects, high costs, and drug resistance, and therefore, the search for new drugs and targets to control this parasite is warranted (3, 4).S-Adenosylmethionine (AdoMet or SAM) 5 is an important biological sulfonium compound recognized as the universal methyl donor for methylation of lipids, proteins, nucleic acids, and xenobiotics in living cells (5). AdoMet is also a donor of propylamine groups for the synthesis of polyamines and participates in the reverse trans-sulfuration pathway where AdoMet is converted into cysteine and glutathione and in Leishmania in the spermidine-glutathione conjugate trypanothione (6, 7). AdoMet is also used as a source of methylene groups, amino groups, and ribosyl groups in the synthesis of fatty acids, biotin, and the modified nucleoside epoxyqueusine of tRNAs (reviewed in Ref. 8).Most cells are capable of synthesizing AdoMet from L-methionine and ATP, in a process requiring the enzyme methionine adenosyltransferase (MAT). The gene coding for this enzyme is present in most sequenced organisms (reviewed in Ref. 9). However, in some Rickettsia strains, the MAT gene is inactivated by a mutation (10), and in the fungus Pneumocystis carinii, no MAT activity has been detected (11). These organisms have the rare distinction of meeting their AdoMet needs by importing it (12). The Rickettsia transporter is part of the drug/ metabolite transporter superfamily (10), and the identity of the Pneumocystis transporter is not known. Transport of AdoMet across the plasma membrane does not occur to a signifi...