nucleobase transport proteins

..Expression of TbNBT1 in Xenopus oocytes further confirmed that this gene encodes the first high affinity nucleobase transporter from protozoa or animals to be identified at the molecular level...

..We finally show that intramolecular synergy among UapA domains is highly specific and propose that it forms the basis for the evolution of the unique specificity of UapA for uric acid, a property not present in other NAT members...

..The results indicate that nucleobases enter the intraerythrocytic parasite via a rapid, equilibrative process that has kinetic characteristics similar to those of PfENT1...

..Recent studies are increasingly addressing the structure and substrate recognition mechanisms of these vital transport proteins...

..Our results are in agreement with a topological model of UapA built on the recently published structure of UraA, a bacterial homolog of UapA...

..Apart from highlighting how a basic process such as nucleobase recognition and transport operates, this review intends to highlight features that might be applicable to antifungal pharmacology...

..The phenotypes of these null mutants underscore the importance of purine nucleobase transporters in the Leishmania life cycle and pharmacology...

..This model, which rationalizes the unique specificity of FurD for uracil, is compared to and found to be very similar to analogous models for protozoan uracil transporters...

..The increased spatial and temporal resolution of the purine biosensor measurements has revealed the complexity of the control of adenosine and purine tone in the cerebellum...

..The work by Gudin et al. characterizes the dynamics of these transporters and points to further areas for future genetic and therapeutic experiments...

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..Among these, Tpn1, Fur4 and the one encoded by yOR071c were found to contribute significantly to 5-FC toxicity, thus revealing alternative entry routes for 5-FC via other cytosine/adenine permease homologues...

..In conclusion, it was suggested that there might be purine- or pyrimidine-selective nucleobase transporters in rat Sertoli cells...

..Both Xut1 and UapA recognize oxypurinol, but use different interactions reflected in a nearly 26-fold difference in their affinities for this drug, while YgfO interacts with this analogue very inefficiently...

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..The results of this study provide molecular evidence that inactivation of the sole FCY2 gene promotes cross-resistance to the antifungal association 5FC-FLC in C. lusitaniae...

..These results provide further support for the occurrence of endocytosis and the lysosomal-endosomal function of the vacuolar compartment in A. nidulans...

..Understanding the nucleoside and nucleobase transporter profiles in the vasculature will allow for further study into their roles in pathophysiological conditions such as hypoxia or ischemia...

..The findings suggest that Ile-432 and Asn-430 of helix XII are crucial for purine uptake and affinity, and Asn-430 is probably at the vicinity of the binding site...

..Subsequently, a combination of 5FC and another antifungal drug is applicable for treating infections of C. tropicalis...

..Thus mouse MVECs from transgenic animals may prove to be a useful preclinical model for studies of the effects of purine metabolite modifiers on vascular function...

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..This may have a biological and evolutional meaning in the transport and metabolism of nucleobases. The present study provides novel insights into the specific transport and metabolism of nucleobases and their analogs for therapeutic use...

..Finally, one of the 17 assayable single-Cys mutants, Q258C, was sensitive to inactivation by N-ethylmaleimide. The findings suggest that polar residues important for the function of YgfO cluster in TMs 1, 3, 8 and 9a...

..These observations imply that LmaNT3 and LmaNT4 are nucleobase/proton symporters...

..These results suggested that there are distinct transport systems for purine and pyrimidine nucleobases in cells of mouse Sertoli cell line TM4...

..Radio-labeled purine uptake experiments in yeast and in planta confirm the function of AtAzg1 and AtAzg2 as plant adenine-guanine transporters...

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..This transporter is potentially important for transporting naturally occurring purines and purine analog drugs into cells...

..Finally, we also discuss how modelling NAT-purine interactions might constitute a step towards the use of NAT proteins as specific gateways for targeting pathogenic microbes...

..FcyB-GFP was also shown to be downregulated by endocytosis in response to ammonia or the presence of cytosine. The expression profile of FcyB supports that its main physiological role is cytosine-purine scavenging...

..Overall, the results show that, like purine nucleobase transport, pyrimidine nucleobase transport function is very similar in L. major and T. brucei insect forms...

..This study shows that transport-related resistance to purine antimetabolites is not easily induced in Trypanosoma spp. as long as uptake is mediated by multiple transporters...

..Thus, these specific pauses might reflect a translational control over membrane protein targeting or early recognition ('+45 pause'), and over insertion or folding ('+70 pause')...

..They also show that the P376 residue is part of an unusual secondary structure, probably a beta-turn motif, which must play a crucial dynamic role in the translocation process...

..The location and the observed decrease in the turnover of the carrier observed with the S272 L change lead us to propose that S272 could be part of a hydrophilic pore involved in the translocation of the base and/or the proton...

..Finally, no specific role of K+ ions on cytosine transport could be demonstrated in this system...

..This result suggests that the 371-377 segment might play a key role in the proper three-dimensional structure of the active purine-cytosine permease...

..By means of thermosensitive secretory-pathway-mutant strains, we demonstrated that purine/cytosine permease phosphorylation occurred either between the Golgi apparatus and the plasma membrane or in the plasma membrane itself...

..These results demonstrate the specificity of the antisera and also suggest that the 45 kDa and 50 kDa proteins are both products of the FCY2 gene...

..glabrata. This differs from the purine cytosine permeases in Saccharomyces cerevisiae and Candida albicans which transport adenine, cytosine, guanine and hypoxanthine...

..Comparisons of the sequences and hydropathy profiles of members of this novel family of transporters yield insights into their structure, functionally important residues, and possible evolutionary relationships...

..Therefore this polypeptide corresponds to the purine-cytosine permease...

..Expression of the FCY2 gene product requires a functional secretory pathway and is reduced in mnn9, a mutant strain deficient in outer chain glycosylation. The FCY2 gene was mapped on the right arm of chromosome V close to the HIS1 gene...

..Therefore, we conclude that modification in the Ktapp of uptake in the strain carrying fcy2-21 allele is merely due to a modification of the binding ability of the permease for its ligands...

..9). The pK of this group remained similar to the value obtained with pAB4 when hypoxanthine was bound. From these data, it is proposed that the binding of hypoxanthine and H+ is a random process...

..In particular, amino acids at position 374 and 377 modulate the affinity of the permease towards its substrates. In the wild-type, when asparagine is present at both of these positions, the lowest Kmapp values are found...

..This promoter appears to be constitutive in various conditions tested. Its five transcription start sites have been mapped, and a derivative expression vector for K. marxianus has been constructed...

..This work represents the development of a new model system for the functional production of recombinant nucleoside transporters of the CNT family of membrane proteins...

..We show that these compounds display a remarkable selectivity for the parasite's transporters. The adenine analogue showed greater trypanocidal activity than the hypoxanthine or guanine analogues in vitro...

..Similar results have been found in studies on the expression of other transporters in A. nidulans, suggesting that global expression of transporters might operate as a general system for sensing solute availability...

..5, 8.5 +/- 0.6, 8.5 +/- 1.1, and 8.8 +/- 4.0 microM, respectively. LmaNT3 is, thus, the first member of the ENT family identified in any organism that functions as a nucleobase rather than nucleoside or nucleoside/nucleobase transporter...

..1 mRNA is significantly more abundant in insect stage procyclic forms than in mammalian stage bloodstream forms, and the TbNT8.1 permease thus may represent a major route for purine nucleobase uptake in procyclic trypanosomes...

..gondii...

..A possible mechanism of this novel phenomenon is outlined...

..In this study, we developed a plasmid-based system that generated a number of affinity-mutated alleles, enabling us to define new amino acids critical for permease function...

..Nodule-enhanced expression was confirmed experimentally for the TCs composed of five or more ESTs, whereas the results for those TCs containing fewer ESTs were variable...

..These findings represent the first demonstration of active Na(+) gradient-dependent nucleobase transport in intestinal brush border membrane vesicles...

..It is proposed that the architecture of their respective binding sites is very similar and that LmNBT1 can be named a functional homolog of TbH2...

..In summary, three closely related PUPs are differentially expressed in Arabidopsis and at least two PUPs have properties similar to the adenine and cytokinin transport system identified in Arabidopsis cell cultures...

..4 mM, positions 323-329 are highly sensitive, with IC(50) values of 15-80 microM, and sensitivity of positions 330-340 follows a periodicity, with mutants sensitive to inactivation clustering on one face of an alpha-helix...

..The reciprocal opening and closing of these cavities is synchronized by the inverted repeat helices 3 and 8, providing the structural basis of the alternating access model for membrane transport...

..Using the appropriate transporter inhibitors, the role of each of these salvage pathways to the overall purine transport in intraerythrocytic Plasmodium falciparum was systematically investigated...

..A single resistant isolate, lacking the above polymorphism in FUR1, has a homozygous polymorphism in FCA1 that results in a glycine-to-aspartate substitution at position 28 in cytosine deaminase...

..The essential roles that purine nucleoside/nucleobase transporters play in parasite viability further suggests selective inhibition of these transporters could be exploited to develop novel drugs against parasitic diseases. ..

..These studies will initiate the molecular analysis of amino acid transporters in Leishmania. ..

..Overall, this proposal will provide a detailed biochemical and genetic dissection of glucose transporter function and the essential role of these permeases in the parasite life cycle. ..

..We will determine the ligand specificity and affinities for LmaNT4 and evaluate LmaNT4 expression throughout the L. major life cycle. ..

..Since glucose is an essential nutrient for these parasites, such compounds would kill the parasite and could act as novel drugs for treatment of the diseases they cause. ..

..The goal of our biomedical work is to define unique features of trypanosome biology and then to exploit these traits for the design of anti-parasitic chemotherapies. ..

..brucei chromosome 2. We have recently developed a preinitiation complex formation assay, a Chromatin Immunoprecipation assay and a yeast two-hybrid system that are pertinent tools for our transcriptional dissections. ..

..We have recently developed a cell-free system that is competent for both of these enzymatic activities. This work is a key first step in our proposed experimental plan. ..

..Overall, this proposal will provide a detailed biochemical and genetic dissection of glucose transporter function and the essential role of these permeases in the parasite life cycle. ..

..The goal of our biomedical work is to define unique features of trypanosome biology and then to exploit these traits for the design of anti-parasitic chemotherapies. ..

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..donovani and oocytes, to determine whether either transporter recognizes melarsoprol or pentamidine, and to discover whether three truncated versions of TbNT1 and TbNT2 encode functional nucleoside transporters. ..

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..These analyses, which will include gene cloning and protein function studies, will help identify the specific mechanisms that trypanosomes employ to accomplish this fundamental cellular process. ..

..These experiments will initiate a detailed molecular study of these biochemically and pharmacologically important transporters in these purine auxotrophic parasites. ..

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