1
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Weng J, Zhou X, Wiriyasermkul P, Ren Z, Chen K, Gil-Iturbe E, Zhou M, Quick M. Insight into the mechanism of H +-coupled nucleobase transport. Proc Natl Acad Sci U S A 2023; 120:e2302799120. [PMID: 37549264 PMCID: PMC10438392 DOI: 10.1073/pnas.2302799120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 07/07/2023] [Indexed: 08/09/2023] Open
Abstract
Members of the nucleobase/ascorbic acid transporter (NAT) gene family are found in all kingdoms of life. In mammals, the concentrative uptake of ascorbic acid (vitamin C) by members of the NAT family is driven by the Na+ gradient, while the uptake of nucleobases in bacteria is powered by the H+ gradient. Here, we report the structure and function of PurTCp, a NAT family member from Colwellia psychrerythraea. The structure of PurTCp was determined to 2.80 Å resolution by X-ray crystallography. PurTCp forms a homodimer, and each protomer has 14 transmembrane segments folded into a transport domain (core domain) and a scaffold domain (gate domain). A purine base is present in the structure and defines the location of the substrate binding site. Functional studies reveal that PurTCp transports purines but not pyrimidines and that purine binding and transport is dependent on the pH. Mutation of a conserved aspartate residue close to the substrate binding site reveals the critical role of this residue in H+-dependent transport of purines. Comparison of the PurTCp structure with transporters of the same structural fold suggests that rigid-body motions of the substrate-binding domain are central for substrate translocation across the membrane.
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Affiliation(s)
- Jun Weng
- Department of Physiology and Cellular Biophysics, Columbia University Irving Medical Center, New York, NY10032
| | - Xiaoming Zhou
- Department of Physiology and Cellular Biophysics, Columbia University Irving Medical Center, New York, NY10032
- Department of Psychiatry, Columbia University Irving Medical Center, New York, NY10032
| | - Pattama Wiriyasermkul
- Department of Psychiatry, Columbia University Irving Medical Center, New York, NY10032
| | - Zhenning Ren
- Verna and Marrs McLean Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX77030
| | - Kehan Chen
- Verna and Marrs McLean Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX77030
| | - Eva Gil-Iturbe
- Department of Psychiatry, Columbia University Irving Medical Center, New York, NY10032
| | - Ming Zhou
- Department of Physiology and Cellular Biophysics, Columbia University Irving Medical Center, New York, NY10032
- Verna and Marrs McLean Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX77030
| | - Matthias Quick
- Department of Physiology and Cellular Biophysics, Columbia University Irving Medical Center, New York, NY10032
- Department of Psychiatry, Columbia University Irving Medical Center, New York, NY10032
- Area Neuroscience - Molecular Therapeutics, New York State Psychiatric Institute, New York, NY10032
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2
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Liao G, Xu Q, Allan AC, Xu X. L-Ascorbic acid metabolism and regulation in fruit crops. PLANT PHYSIOLOGY 2023; 192:1684-1695. [PMID: 37073491 PMCID: PMC10315321 DOI: 10.1093/plphys/kiad241] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 04/03/2023] [Accepted: 04/10/2023] [Indexed: 05/03/2023]
Abstract
L-Ascorbic acid (AsA) is more commonly known as vitamin C and is an indispensable compound for human health. As a major antioxidant, AsA not only maintains redox balance and resists biological and abiotic stress but also regulates plant growth, induces flowering, and delays senescence through complex signal transduction networks. However, AsA content varies greatly in horticultural crops, especially in fruit crops. The AsA content of the highest species is approximately 1,800 times higher than that of the lowest species. There have been significant advancements in the understanding of AsA accumulation in the past 20 years. The most noteworthy accomplishment was the identification of the critical rate-limiting genes for the 2 major AsA synthesis pathways (L-galactose pathway and D-galacturonic acid pathway) in fruit crops. The rate-limiting genes of the former are GMP, GME, GGP, and GPP, and the rate-limiting gene of the latter is GalUR. Moreover, APX, MDHAR, and DHAR are also regarded as key genes in degradation and regeneration pathways. Interestingly, some of these key genes are sensitive to environmental factors, such as GGP being induced by light. The efficiency of enhancing AsA content is high by editing upstream open reading frames (uORF) of the key genes and constructing multi-gene expression vectors. In summary, the AsA metabolism has been well understood in fruit crops, but the transport mechanism of AsA and the synergistic improvement of AsA and other traits is less known, which will be the focus of AsA research in fruit crops.
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Affiliation(s)
- Guanglian Liao
- National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, Hubei 430070, PR China
- Kiwifruit Institute, Jiangxi Agricultural University, Nanchang, Jiangxi 330045, PR China
| | - Qiang Xu
- National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, Hubei 430070, PR China
| | - Andrew C Allan
- The New Zealand Institute for Plant and Food Research Limited (Plant & Food Research) Mt Albert, Private Bag 92169, Auckland Mail Centre, Auckland 1142, New Zealand
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
| | - Xiaobiao Xu
- Kiwifruit Institute, Jiangxi Agricultural University, Nanchang, Jiangxi 330045, PR China
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3
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Wang M, He J, Li S, Cai Q, Zhang K, She J. Structural basis of vitamin C recognition and transport by mammalian SVCT1 transporter. Nat Commun 2023; 14:1361. [PMID: 36914666 PMCID: PMC10011568 DOI: 10.1038/s41467-023-37037-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 02/28/2023] [Indexed: 03/15/2023] Open
Abstract
Vitamin C (L-ascorbic acid) is an essential nutrient for human health, and its deficiency has long been known to cause scurvy. Sodium-dependent vitamin C transporters (SVCTs) are responsible for vitamin C uptake and tissue distribution in mammals. Here, we present cryogenic electron microscopy structures of mouse SVCT1 in both the apo and substrate-bound states. Mouse SVCT1 forms a homodimer with each protomer containing a core domain and a gate domain. The tightly packed extracellular interfaces between the core domain and gate domain stabilize the protein in an inward-open conformation for both the apo and substrate-bound structures. Vitamin C binds at the core domain of each subunit, and two potential sodium ions are identified near the binding site. The coordination of sodium ions by vitamin C explains their coupling transport. SVCTs probably deliver substrate through an elevator mechanism in combination with local structural arrangements. Altogether, our results reveal the molecular mechanism by which SVCTs recognize vitamin C and lay a foundation for further mechanistic studies on SVCT substrate transport.
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Affiliation(s)
- Mingxing Wang
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Biomedical Sciences and Health Laboratory of Anhui Province, University of Science and Technology of China, Hefei, 230026, China
| | - Jin He
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Biomedical Sciences and Health Laboratory of Anhui Province, University of Science and Technology of China, Hefei, 230026, China
| | - Shanshan Li
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
- Biomedical Sciences and Health Laboratory of Anhui Province, University of Science and Technology of China, Hefei, 230026, China
| | - Qianwen Cai
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China
| | - Kaiming Zhang
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China.
- Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China.
- Biomedical Sciences and Health Laboratory of Anhui Province, University of Science and Technology of China, Hefei, 230026, China.
| | - Ji She
- MOE Key Laboratory for Cellular Dynamics, Hefei National Research Center for Interdisciplinary Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China.
- Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230026, China.
- Biomedical Sciences and Health Laboratory of Anhui Province, University of Science and Technology of China, Hefei, 230026, China.
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4
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Tatsaki E, Anagnostopoulou E, Zantza I, Lazou P, Mikros E, Frillingos S. Identification of New Specificity Determinants in Bacterial Purine Nucleobase Transporters based on an Ancestral Sequence Reconstruction Approach. J Mol Biol 2021; 433:167329. [PMID: 34710398 DOI: 10.1016/j.jmb.2021.167329] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 10/05/2021] [Accepted: 10/19/2021] [Indexed: 11/28/2022]
Abstract
The relation of sequence with specificity in membrane transporters is challenging to explore. Most relevant studies until now rely on comparisons of present-day homologs. In this work, we study a set of closely related transporters by employing an evolutionary, ancestral-reconstruction approach and reveal unexpected new specificity determinants. We analyze a monophyletic group represented by the xanthine-specific XanQ of Escherichia coli in the Nucleobase-Ascorbate Transporter/Nucleobase-Cation Symporter-2 (NAT/NCS2) family. We reconstructed AncXanQ, the putative common ancestor of this clade, expressed it in E. coli K-12, and found that, in contrast to XanQ, it encodes a high-affinity permease for both xanthine and guanine, which also recognizes adenine, hypoxanthine, and a range of analogs. AncXanQ conserves all binding-site residues of XanQ and differs substantially in only five intramembrane residues outside the binding site. We subjected both homologs to rationally designed mutagenesis and present evidence that these five residues are linked with the specificity change. In particular, we reveal Ser377 of XanQ (Gly in AncXanQ) as a major determinant. Replacement of this Ser with Gly enlarges the specificity of XanQ towards an AncXanQ-phenotype. The ortholog from Neisseria meningitidis retaining Gly at this position is also a xanthine/guanine transporter with extended substrate profile like AncXanQ. Molecular Dynamics shows that the S377G replacement tilts transmembrane helix 12 resulting in rearrangement of Phe376 relative to Phe94 in the XanQ binding pocket. This effect may rationalize the enlarged specificity. On the other hand, the specificity effect of S377G can be masked by G27S or other mutations through epistatic interactions.
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Affiliation(s)
- Ekaterini Tatsaki
- Laboratory of Biological Chemistry, Department of Medicine, School of Health Sciences, University of Ioannina, Ioannina, Greece
| | - Eleni Anagnostopoulou
- Laboratory of Biological Chemistry, Department of Medicine, School of Health Sciences, University of Ioannina, Ioannina, Greece. https://twitter.com/EleniAnagn
| | - Iliana Zantza
- Division of Pharmaceutical Chemistry, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens, Greece
| | - Panayiota Lazou
- Laboratory of Biological Chemistry, Department of Medicine, School of Health Sciences, University of Ioannina, Ioannina, Greece
| | - Emmanuel Mikros
- Division of Pharmaceutical Chemistry, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens, Greece
| | - Stathis Frillingos
- Laboratory of Biological Chemistry, Department of Medicine, School of Health Sciences, University of Ioannina, Ioannina, Greece; Institute of Biosciences, University Research Center of Ioannina, Ioannina, Greece.
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5
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Diallinas G. Transporter Specificity: A Tale of Loosened Elevator-Sliding. Trends Biochem Sci 2021; 46:708-717. [PMID: 33903007 DOI: 10.1016/j.tibs.2021.03.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Revised: 03/13/2021] [Accepted: 03/26/2021] [Indexed: 12/14/2022]
Abstract
Elevator-type transporters are a group of proteins translocating nutrients and metabolites across cell membranes. Despite structural and functional differences, elevator-type transporters use a common mechanism of substrate translocation via reversible movements of a mobile core domain (the elevator), which includes the substrate binding site, along a rigid scaffold domain, stably anchored in the plasma membrane. How substrate specificity is determined in elevator transporters remains elusive. Here, I discuss how a recent report on the sliding elevator mechanism, seen under the context of genetic analysis of a prototype fungal transporter, sheds light on how specificity might be genetically modified. I propose that flexible specificity alterations might occur by 'loosening' of the sliding mechanism from tight coupling to substrate binding.
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Affiliation(s)
- George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, 15784, Athens, Greece; Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion, Greece.
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6
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Context-dependent Cryptic Roles of Specific Residues in Substrate Selectivity of the UapA Purine Transporter. J Mol Biol 2021; 433:166814. [PMID: 33497644 DOI: 10.1016/j.jmb.2021.166814] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 12/29/2020] [Accepted: 01/04/2021] [Indexed: 12/22/2022]
Abstract
Members of the ubiquitous Nucleobase Ascorbate Transporter (NAT) family are H+ or Na+ symporters specific for the cellular uptake of either purines and pyrimidines or L-ascorbic acid. Despite the fact that several bacterial and fungal members have been extensively characterised at a genetic, biochemical or cellular level, and crystal structures of NAT members from Escherichia coli and Aspergillus nidulans have been determined pointing to a mechanism of transport, we have little insight on how substrate selectivity is determined. Here, we present systematic mutational analyses, rational combination of mutations, and novel genetic screens that reveal cryptic context-dependent roles of partially conserved residues in the so-called NAT signature motif in determining the specificity of the UapA transporter of A. nidulans. We show that specific NAT signature motif substitutions, alone and in combinations with each other or with distant mutations in residues known to affect substrate selectivity, lead to novel UapA versions possessing variable transport capacities and specificities for nucleobases. In particular, we show that a UapA version including the quadruple mutation T405S/F406Y/A407S/Q408E in the NAT signature motif (UapA-SYSE) becomes incapable of purine transport, but gains a novel pyrimidine-related profile, which can be further altered to a more promiscuous purine/pyrimidine profile when combined with replacements at distantly located residues, especially at F528. Our results reveal that UapA specificity is genetically highly modifiable and allow us to speculate on how the elevator-type mechanism of transport might account for this flexibility.
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7
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Sun T, Pei T, Yang L, Zhang Z, Li M, Liu Y, Ma F, Liu C. Exogenous application of xanthine and uric acid and nucleobase-ascorbate transporter MdNAT7 expression regulate salinity tolerance in apple. BMC PLANT BIOLOGY 2021; 21:52. [PMID: 33468049 PMCID: PMC7816448 DOI: 10.1186/s12870-021-02831-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 01/07/2021] [Indexed: 05/05/2023]
Abstract
BACKGROUND Soil salinity is a critical threat to global agriculture. In plants, the accumulation of xanthine activates xanthine dehydrogenase (XDH), which catalyses the oxidation/conversion of xanthine to uric acid to remove excess reactive oxygen species (ROS). The nucleobase-ascorbate transporter (NAT) family is also known as the nucleobase-cation symporter (NCS) or AzgA-like family. NAT is known to transport xanthine and uric acid in plants. The expression of MdNAT is influenced by salinity stress in apple. RESULTS In this study, we discovered that exogenous application of xanthine and uric acid enhanced the resistance of apple plants to salinity stress. In addition, MdNAT7 overexpression transgenic apple plants showed enhanced xanthine and uric acid concentrations and improved tolerance to salinity stress compared with nontransgenic plants, while opposite phenotypes were observed for MdNAT7 RNAi plants. These differences were probably due to the enhancement or impairment of ROS scavenging and ion homeostasis abilities. CONCLUSION Our results demonstrate that xanthine and uric acid have potential uses in salt stress alleviation, and MdNAT7 can be utilized as a candidate gene to engineer resistance to salt stress in plants.
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Affiliation(s)
- Tingting Sun
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
- Beijing Academy of Forestry and Pomology Sciences, Beijing Engineering Research Center for Deciduous Fruit Trees, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Ministry of Agriculture and Rural Affairs, Beijing, 100093, People's Republic of China
| | - Tingting Pei
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
| | - Lulu Yang
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
| | - Zhijun Zhang
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
| | - Mingjun Li
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
| | - Yuerong Liu
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China
| | - Fengwang Ma
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China.
| | - Changhai Liu
- State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China.
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8
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Botou M, Yalelis V, Lazou P, Zantza I, Papakostas K, Charalambous V, Mikros E, Flemetakis E, Frillingos S. Specificity profile of NAT/NCS2 purine transporters in
Sinorhizobium
(
Ensifer
)
meliloti. Mol Microbiol 2020; 114:151-171. [DOI: 10.1111/mmi.14503] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Revised: 03/16/2020] [Indexed: 02/06/2023]
Affiliation(s)
- Maria Botou
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
| | - Vassilis Yalelis
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
| | - Panayiota Lazou
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
| | - Iliana Zantza
- Division of Pharmaceutical Chemistry Department of Pharmacy School of Health Sciences National and Kapodistrian University of Athens Athens Greece
| | - Konstantinos Papakostas
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
| | - Vassiliki Charalambous
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
| | - Emmanuel Mikros
- Division of Pharmaceutical Chemistry Department of Pharmacy School of Health Sciences National and Kapodistrian University of Athens Athens Greece
| | - Emmanouil Flemetakis
- Laboratory of Molecular Biology Department of Biotechnology Agricultural University of Athens Athens Greece
| | - Stathis Frillingos
- Laboratory of Biological Chemistry Department of Medicine School of Health Sciences University of Ioannina Ioannina Greece
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9
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Stoffer-Bittner AJ, Alexander CR, Dingman DW, Mourad GS, Schultes NP. Functional characterization of the uracil transporter from honeybee pathogen Paenibacillus larvae. Microb Pathog 2018; 124:305-310. [DOI: 10.1016/j.micpath.2018.08.059] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 08/25/2018] [Indexed: 11/30/2022]
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10
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Stoffer‐Bittner AJ, Alexander CR, Dingman DW, Mourad GS, Schultes NP. The solute transport and binding profile of a novel nucleobase cation symporter 2 from the honeybee pathogen Paenibacillus larvae. FEBS Open Bio 2018; 8:1322-1331. [PMID: 30087835 PMCID: PMC6070649 DOI: 10.1002/2211-5463.12488] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 06/22/2018] [Accepted: 06/24/2018] [Indexed: 11/29/2022] Open
Abstract
Here, we report that a novel nucleobase cation symporter 2 encoded in the genome of the honeybee bacterial pathogen Paenibacillus larvae reveals high levels of amino acid sequence similarity to the Escherichia coli and Bacillus subtilis uric acid and xanthine transporters. This transporter is named P. larvae uric acid permease-like protein (PlUacP). Even though PlUacP displays overall amino acid sequence similarities, has common secondary structures, and shares functional motifs and functionally important amino acids with E. coli xanthine and uric acid transporters, these commonalities are insufficient to assign transport function to PlUacP. The solute transport and binding profile of PlUacP was determined by radiolabeled uptake experiments via heterologous expression in nucleobase transporter-deficient Saccharomyces cerevisiae strains. PlUacP transports the purines adenine and guanine and the pyrimidine uracil. Hypoxanthine, xanthine, and cytosine are not transported by PlUacP, but, along with uric acid, bind in a competitive manner. PlUacP has strong affinity for adenine Km 7.04 ± 0.18 μm, and as with other bacterial and plant NCS2 proteins, PlUacP function is inhibited by the proton disruptor carbonyl cyanide m-chlorophenylhydrazone. The solute transport and binding profile identifies PlUacP as a novel nucleobase transporter.
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Affiliation(s)
| | | | - Douglas W. Dingman
- Department of EntomologyThe Connecticut Agricultural Experiment StationNew HavenCTUSA
| | - George S. Mourad
- Department of BiologyIndiana University‐Purdue University Fort WayneINUSA
| | - Neil P. Schultes
- Department of Plant Pathology & EcologyThe Connecticut Agricultural Experiment StationNew HavenCTUSA
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11
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Kourkoulou A, Pittis AA, Diallinas G. Evolution of substrate specificity in the Nucleobase-Ascorbate Transporter (NAT) protein family. MICROBIAL CELL 2018; 5:280-292. [PMID: 29850465 PMCID: PMC5972032 DOI: 10.15698/mic2018.06.636] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
L-ascorbic acid (vitamin C) is an essential metabolite in animals and plants due to its role as an enzyme co-factor and antioxidant activity. In most eukaryotic organisms, L-ascorbate is biosynthesized enzymatically, but in several major groups, including the primate suborder Haplorhini, this ability is lost due to gene truncations in the gene coding for L-gulonolactone oxidase. Specific ascorbate transporters (SVCTs) have been characterized only in mammals and shown to be essential for life. These belong to an extensively studied transporter family, called Nucleobase-Ascorbate Transporters (NAT). The prototypic member of this family, and one of the most extensively studied eukaryotic transporters, is UapA, a uric acid-xanthine/H+ symporter in the fungus Aspergillus nidulans. Here, we investigate molecular aspects of NAT substrate specificity and address the evolution of ascorbate transporters apparently from ancestral nucleobase transporters. We present a phylogenetic analysis, identifying a distinct NAT clade that includes all known L-ascorbate transporters. This clade includes homologues only from vertebrates, and has no members in non-vertebrate or microbial eukaryotes, plants or prokaryotes. Additionally, we identify within the substrate-binding site of NATs a differentially conserved motif, which we propose is critical for nucleobase versus ascorbate recognition. This conclusion is supported by the amino acid composition of this motif in distinct phylogenetic clades and mutational analysis in the UapA transporter. Together with evidence obtained herein that UapA can recognize with extremely low affinity L-ascorbate, our results support that ascorbate-specific NATs evolved by optimization of a sub-function of ancestral nucleobase transporters.
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Affiliation(s)
- Anezia Kourkoulou
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens 15784, Greece
| | | | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens 15784, Greece
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12
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Alexander CR, Dingman DW, Schultes NP, Mourad GS. The solute transport profile of two Aza-guanine transporters from the Honey bee pathogen Paenibacillus larvae. FEMS Microbiol Lett 2018; 365:4828326. [DOI: 10.1093/femsle/fny018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 01/26/2018] [Indexed: 01/05/2023] Open
Affiliation(s)
- Candace R Alexander
- Department of Biology, Indiana University-Purdue University Fort Wayne, 2101 East Coliseum Blvd., Fort Wayne, IN 46805, USA
| | - Douglas W Dingman
- Department of Entomology, The Connecticut Agricultural Experiment Station, 123 Huntington St, New Haven, CT 06511, USA
| | - Neil P Schultes
- Department of Plant Pathology & Ecology, The Connecticut Agricultural Experiment Station, 123 Huntington St, New Haven, CT 06511, USA
| | - George S Mourad
- Department of Biology, Indiana University-Purdue University Fort Wayne, 2101 East Coliseum Blvd., Fort Wayne, IN 46805, USA
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13
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Balaska S, Myrianthopoulos V, Tselika M, Hatzinikolaou DG, Mikros E, Diallinas G. NmeA, a novel efflux transporter specific for nucleobases and nucleosides, contributes to metal resistance in Aspergillus nidulans. Mol Microbiol 2017; 105:426-439. [PMID: 28509393 DOI: 10.1111/mmi.13708] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/12/2017] [Indexed: 01/01/2023]
Abstract
Through Minos transposon mutagenesis we obtained A. nidulans mutants resistant to 5-fluorouracil due to insertions into the upstream region of the uncharacterized gene nmeA, encoding a Major Facilitator Superfamily (MFS) transporter. Minos transpositions increased nmeA transcription, which is otherwise extremely low under all conditions tested. To dissect the function of NmeA we used strains overexpressing or genetically lacking the nmeA gene. Strains overexpressing NmeA are resistant to toxic purine analogues, but also, to cadmium, zinc and borate, whereas an isogenic nmeAΔ null mutant exhibits increased sensitivity to these compounds. We provide direct evidence that nmeA overexpression leads to efflux of adenine, xanthine, uric acid and allantoin, the latter two being intermediate metabolites of purine catabolism that are toxic when accumulated cytoplasmically due to relevant genetic lesions. By using a functional GFP-tagged version we show that NmeA is a plasma membrane transporter. Homology modeling and docking approaches identified a single purine binding site and a tentative substrate translocation trajectory in NmeA. Orthologues of NmeA are present in all Aspergilli and other Eurotiomycetes, but are absent from other fungi or non-fungal organisms. NmeA is thus the founding member of a new class of transporters essential for fungal success under specific toxic conditions.
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Affiliation(s)
- Sofia Balaska
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15784, Greece
| | - Vassilios Myrianthopoulos
- Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15771, Greece
| | - Martha Tselika
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15784, Greece
| | - Dimitris G Hatzinikolaou
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15784, Greece
| | - Emmanuel Mikros
- Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15771, Greece
| | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, 15784, Greece
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Barraco-Vega M, Romero H, Richero M, Cerdeiras MP, Cecchetto G. Functional characterization of two novel purine transporters from the Basidiomycota Phanerochaete chrysosporium. Gene 2017; 601:1-10. [PMID: 27923672 DOI: 10.1016/j.gene.2016.11.033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 11/07/2016] [Accepted: 11/17/2016] [Indexed: 12/24/2022]
Abstract
Purine transporters as substrate entry points in organisms, are involved in a number of cellular processes such as nitrogen source uptake, energy metabolism and synthesis of nucleic acids. In this study, two nucleobase transporter genes (phZ, phU) from Phanerochaete chrysosporium were cloned, identified, and functionally characterized. Our results show that PhZ is a transporter of adenine and hypoxanthine, and a protein belonging to the AzgA-like family, whilst PhU belongs to the NAT/NCS2 family, transporting xanthine and uric acid. No other sequences belonging to these families were detected in P. chrysosporium's genome. Phylogenetic analyses show that AzgA-like sequences form monophyletic groups for each major lineage (Ascomycota, Basidiomycota and Zygomycota). In contrast, Ascomycota and Basidiomycota NAT/NCS2 sequences do not form monophyletic groups and several copies of this protein are distributed across the tree. Expression of phU was significantly downregulated in the presence of a primary source like ammonium, and enhanced if purines were present or if the mycelium was nitrogen starved. phZ was clearly induced by its substrates (hypoxanthine, adenine), very lightly induced by xanthine, suppressed by urea and amino acids and expressed at a basal level when uric acid or ammonium was the nitrogen source or when the mycelium was starved for nitrogen. In order to perform substrate analyses, both P. chrysosporium proteins (PhZ, PhU) were expressed in Aspergillus nidulans. Epifluorescent microscopy showed that under inducing conditions, PhZ-GFP and PhU-GFP were present at the plasma membrane of A. nidulans transformed strains, and were internalized in repressed conditions. Our results suggest that in the white-rot fungus P. chrysosporium, phU has a catabolic role and phZ, (less dependent of the nitrogen source), plays a key role in purine acquisition to provide biosynthetic components. These are the first purine transporters characterized in Basidiomycota.
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Affiliation(s)
- Mariana Barraco-Vega
- Microbiología Departamento de Biociencias, Facultad de Química, Universidad de la República, Montevideo 11800, Uruguay.
| | - Héctor Romero
- Laboratorio de Organización y Evolución del Genoma, Departamento de Ecología y Evolución, Facultad de Ciencias, Universidad de la República, Montevideo 11400, Uruguay
| | - Mariana Richero
- Microbiología Instituto de Química Biológica, Facultad de Ciencias - Facultad de Química, Universidad de la República, Montevideo 11800, Uruguay
| | - María Pía Cerdeiras
- Microbiología Departamento de Biociencias, Facultad de Química, Universidad de la República, Montevideo 11800, Uruguay
| | - Gianna Cecchetto
- Microbiología Instituto de Química Biológica, Facultad de Ciencias - Facultad de Química, Universidad de la República, Montevideo 11800, Uruguay
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Lougiakis N, Gavriil ES, Kairis M, Sioupouli G, Lambrinidis G, Benaki D, Krypotou E, Mikros E, Marakos P, Pouli N, Diallinas G. Design and synthesis of purine analogues as highly specific ligands for FcyB, a ubiquitous fungal nucleobase transporter. Bioorg Med Chem 2016; 24:5941-5952. [PMID: 27720327 DOI: 10.1016/j.bmc.2016.09.055] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 08/31/2016] [Accepted: 09/21/2016] [Indexed: 01/17/2023]
Abstract
In the course of our study on fungal purine transporters, a number of new 3-deazapurine analogues have been rationally designed, based on the interaction of purine substrates with the Aspergillus nidulans FcyB carrier, and synthesized following an effective synthetic procedure. Certain derivatives have been found to specifically inhibit FcyB-mediated [3H]-adenine uptake. Molecular simulations have been performed, suggesting that all active compounds interact with FcyB through the formation of hydrogen bonds with Asn163, while the insertion of hydrophobic fragments at position 9 and N6 of 3-deazaadenine enhanced the inhibition.
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Affiliation(s)
- Nikolaos Lougiakis
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Efthymios-Spyridon Gavriil
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Markelos Kairis
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Georgia Sioupouli
- Department of Biology, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 15784, Greece
| | - George Lambrinidis
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Dimitra Benaki
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Emilia Krypotou
- Department of Biology, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 15784, Greece
| | - Emmanuel Mikros
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Panagiotis Marakos
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece
| | - Nicole Pouli
- Division of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Athens 15771, Greece.
| | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 15784, Greece.
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16
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Dissection of Transporter Function: From Genetics to Structure. Trends Genet 2016; 32:576-590. [DOI: 10.1016/j.tig.2016.06.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 06/20/2016] [Accepted: 06/21/2016] [Indexed: 12/20/2022]
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Structure of eukaryotic purine/H(+) symporter UapA suggests a role for homodimerization in transport activity. Nat Commun 2016; 7:11336. [PMID: 27088252 PMCID: PMC4837479 DOI: 10.1038/ncomms11336] [Citation(s) in RCA: 91] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Accepted: 03/16/2016] [Indexed: 02/03/2023] Open
Abstract
The uric acid/xanthine H+ symporter, UapA, is a high-affinity purine transporter from the filamentous fungus Aspergillus nidulans. Here we present the crystal structure of a genetically stabilized version of UapA (UapA-G411VΔ1–11) in complex with xanthine. UapA is formed from two domains, a core domain and a gate domain, similar to the previously solved uracil transporter UraA, which belongs to the same family. The structure shows UapA in an inward-facing conformation with xanthine bound to residues in the core domain. Unlike UraA, which was observed to be a monomer, UapA forms a dimer in the crystals with dimer interactions formed exclusively through the gate domain. Analysis of dominant negative mutants is consistent with dimerization playing a key role in transport. We postulate that UapA uses an elevator transport mechanism likely to be shared with other structurally homologous transporters including anion exchangers and prestin. UapA is a uric acid/xanthine H+ symporter from a filamentous fungus. Here, the authors solve the crystal structure of the transporter in complex with xanthine revealing it to be a dimer, and this homodimerisation is proposed to be important for function.
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Lipid interaction sites on channels, transporters and receptors: Recent insights from molecular dynamics simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2390-2400. [PMID: 26946244 DOI: 10.1016/j.bbamem.2016.02.037] [Citation(s) in RCA: 130] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Revised: 02/25/2016] [Accepted: 02/28/2016] [Indexed: 11/22/2022]
Abstract
Lipid molecules are able to selectively interact with specific sites on integral membrane proteins, and modulate their structure and function. Identification and characterization of these sites are of importance for our understanding of the molecular basis of membrane protein function and stability, and may facilitate the design of lipid-like drug molecules. Molecular dynamics simulations provide a powerful tool for the identification of these sites, complementing advances in membrane protein structural biology and biophysics. We describe recent notable biomolecular simulation studies which have identified lipid interaction sites on a range of different membrane proteins. The sites identified in these simulation studies agree well with those identified by complementary experimental techniques. This demonstrates the power of the molecular dynamics approach in the prediction and characterization of lipid interaction sites on integral membrane proteins. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Targeting the parasite's DNA with methyltriazenyl purine analogs is a safe, selective, and efficacious antitrypanosomal strategy. Antimicrob Agents Chemother 2015; 59:6708-16. [PMID: 26282430 PMCID: PMC4604408 DOI: 10.1128/aac.00596-15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 07/22/2015] [Indexed: 12/04/2022] Open
Abstract
The human and veterinary disease complex known as African trypanosomiasis continues to inflict significant global morbidity, mortality, and economic hardship. Drug resistance and toxic side effects of old drugs call for novel and unorthodox strategies for new and safe treatment options. We designed methyltriazenyl purine prodrugs to be rapidly and selectively internalized by the parasite, after which they disintegrate into a nontoxic and naturally occurring purine nucleobase, a simple triazene-stabilizing group, and the active toxin: a methyldiazonium cation capable of damaging DNA by alkylation. We identified 2-(3-acetyl-3-methyltriazen-1-yl)-6-hydroxypurine (compound 1) as a new lead compound, which showed submicromolar potency against Trypanosoma brucei, with a selectivity index of >500, and it demonstrated a curative effect in animal models of acute trypanosomiasis. We investigated the mechanism of action of this lead compound and showed that this molecule has significantly higher affinity for parasites over mammalian nucleobase transporters, and it does not show cross-resistance with current first-line drugs. Once selectively accumulated inside the parasite, the prodrug releases a DNA-damaging methyldiazonium cation. We propose that ensuing futile cycles of attempted mismatch repair then lead to G2/M phase arrest and eventually cell death, as evidenced by the reduced efficacy of this purine analog against a mismatch repair-deficient (MSH2−/−) trypanosome cell line. The observed absence of genotoxicity, hepatotoxicity, and cytotoxicity against mammalian cells revitalizes the idea of pursuing parasite-selective DNA alkylators as a safe chemotherapeutic option for the treatment of human and animal trypanosomiasis.
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Karena E, Tatsaki E, Lambrinidis G, Mikros E, Frillingos S. Analysis of conserved NCS2 motifs in theEscherichia colixanthine permease XanQ. Mol Microbiol 2015; 98:502-17. [DOI: 10.1111/mmi.13138] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/16/2015] [Indexed: 11/28/2022]
Affiliation(s)
- Ekaterini Karena
- Laboratory of Biological Chemistry; University of Ioannina School of Health Sciences; Ioannina Greece
| | - Ekaterini Tatsaki
- Laboratory of Biological Chemistry; University of Ioannina School of Health Sciences; Ioannina Greece
| | - George Lambrinidis
- Laboratory of Pharmaceutical Chemistry; National and Kapodistrian University of Athens School of Pharmacy; Athens Greece
| | - Emmanuel Mikros
- Laboratory of Pharmaceutical Chemistry; National and Kapodistrian University of Athens School of Pharmacy; Athens Greece
| | - Stathis Frillingos
- Laboratory of Biological Chemistry; University of Ioannina School of Health Sciences; Ioannina Greece
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21
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Martzoukou O, Karachaliou M, Yalelis V, Leung J, Byrne B, Amillis S, Diallinas G. Oligomerization of the UapA Purine Transporter Is Critical for ER-Exit, Plasma Membrane Localization and Turnover. J Mol Biol 2015; 427:2679-96. [DOI: 10.1016/j.jmb.2015.05.021] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Revised: 05/27/2015] [Accepted: 05/28/2015] [Indexed: 11/29/2022]
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Pardridge WM. Blood-brain barrier endogenous transporters as therapeutic targets: a new model for small molecule CNS drug discovery. Expert Opin Ther Targets 2015; 19:1059-72. [PMID: 25936389 DOI: 10.1517/14728222.2015.1042364] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
INTRODUCTION The blood-brain barrier (BBB) limits the uptake of most drugs by brain, and the traditional approach to the BBB problem is the use of medicinal chemistry to increase drug lipid solubility, and increase lipid-mediated transport across the BBB. This review advocates a new model to CNS drug discovery of BBB-penetrating small molecules, whereby drug candidates are screened for carrier-mediated transport (CMT) across the BBB. AREAS COVERED CMT systems are expressed by genes within the Solute Carrier (SLC) Transporter Gene Family, which now totals > 400 transporter genes. Emphasis is placed on reconciliation of the substrate transporter profile (STP) of BBB transport in vivo with the STP of the cloned SLC transporter in vitro. This reconciliation is crucial to the identification, from sometimes a large number of candidates, of the respective SLC transporter that is responsible for BBB transport in vivo for a given class of nutrients. EXPERT OPINION Dual track screening of a small molecule library for drugs that have the dual properties of affinity for a neural cell drug receptor target, and affinity for a BBB CMT transporter target, can lead to a revolution in how small molecule drugs are identified in CNS drug discovery programs.
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Affiliation(s)
- William M Pardridge
- University of California , 1180 Tellem Drive, Pacific Palisades, Los Angeles, CA 90272 , USA +1 310 459 0163 ; +1 310 459 0163 ;
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23
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Krypotou E, Evangelidis T, Bobonis J, Pittis AA, Gabaldón T, Scazzocchio C, Mikros E, Diallinas G. Origin, diversification and substrate specificity in the family of NCS1/FUR transporters. Mol Microbiol 2015; 96:927-50. [DOI: 10.1111/mmi.12982] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/22/2015] [Indexed: 12/19/2022]
Affiliation(s)
- Emilia Krypotou
- Faculty of Biology; University of Athens; Panepistimioupolis Athens 15784 Greece
| | - Thomas Evangelidis
- Faculty of Pharmacy; University of Athens; Panepistimioupolis Athens 15771 Greece
| | - Jacob Bobonis
- Faculty of Biology; University of Athens; Panepistimioupolis Athens 15784 Greece
| | - Alexandros A. Pittis
- Bioinformatics and Genomics Programme; Centre for Genomic Regulation (CRG); Dr. Aiguader, 88 Barcelona 08003 Spain
- Department of Experimental and Health Sciences; Universitat Pompeu Fabra (UPF); Barcelona 08003 Spain
| | - Toni Gabaldón
- Bioinformatics and Genomics Programme; Centre for Genomic Regulation (CRG); Dr. Aiguader, 88 Barcelona 08003 Spain
- Department of Experimental and Health Sciences; Universitat Pompeu Fabra (UPF); Barcelona 08003 Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA); Pg. Lluís Companys 23 Barcelona 08010 Spain
| | - Claudio Scazzocchio
- Department of Microbiology; Imperial College; London SW7 2AZ UK
- Institut de Génétique et Microbiologie; Université Paris-Sud; France
| | - Emmanuel Mikros
- Faculty of Pharmacy; University of Athens; Panepistimioupolis Athens 15771 Greece
| | - George Diallinas
- Faculty of Biology; University of Athens; Panepistimioupolis Athens 15784 Greece
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Kalli AC, Sansom MSP, Reithmeier RAF. Molecular dynamics simulations of the bacterial UraA H+-uracil symporter in lipid bilayers reveal a closed state and a selective interaction with cardiolipin. PLoS Comput Biol 2015; 11:e1004123. [PMID: 25729859 PMCID: PMC4346270 DOI: 10.1371/journal.pcbi.1004123] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 01/09/2015] [Indexed: 11/25/2022] Open
Abstract
The Escherichia coli UraA H+-uracil symporter is a member of the nucleobase/ascorbate transporter (NAT) family of proteins, and is responsible for the proton-driven uptake of uracil. Multiscale molecular dynamics simulations of the UraA symporter in phospholipid bilayers consisting of: 1) 1-palmitoyl 2-oleoyl-phosphatidylcholine (POPC); 2) 1-palmitoyl 2-oleoyl-phosphatidylethanolamine (POPE); and 3) a mixture of 75% POPE, 20% 1-palmitoyl 2-oleoyl-phosphatidylglycerol (POPG); and 5% 1-palmitoyl 2-oleoyl-diphosphatidylglycerol/cardiolipin (CL) to mimic the lipid composition of the bacterial inner membrane, were performed using the MARTINI coarse-grained force field to self-assemble lipids around the crystal structure of this membrane transport protein, followed by atomistic simulations. The overall fold of the protein in lipid bilayers remained similar to the crystal structure in detergent on the timescale of our simulations. Simulations were performed in the absence of uracil, and resulted in a closed state of the transporter, due to relative movement of the gate and core domains. Anionic lipids, including POPG and especially CL, were found to associate with UraA, involving interactions between specific basic residues in loop regions and phosphate oxygens of the CL head group. In particular, three CL binding sites were identified on UraA: two in the inner leaflet and a single site in the outer leaflet. Mutation of basic residues in the binding sites resulted in the loss of CL binding in the simulations. CL may play a role as a “proton trap” that channels protons to and from this transporter within CL-enriched areas of the inner bacterial membrane. Symporters are proteins that are responsible for the co-transport of ions and small molecule solutes across cell membranes. UraA is an example of a symporter, and is responsible for the proton-driven uptake of uracil in bacteria like E. coli. Despite its importance as a member of a large family of nucleobase/ascorbate transporters (NAT) and the existence of structural and functional data, the mechanism by which UraA transports uracil across the bacterial membrane, and in particular the role of its diverse and complex lipid environment in the transport mechanism, remains elusive. In this study, we have used a multiscale computational methodology to examine the dynamics of UraA and to elucidate its interactions with lipids that resemble its native environment in the bacterial inner membrane. Our results demonstrate that negatively-charged lipids in the membrane (phosphatidylglycerol and cardiolipin) associate preferentially with UraA and may play a role in its function. Additionally, our simulations resulted in a closed state of UraA, a likely intermediate in the transport mechanism that may not be readily accessible by experimental methods.
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Affiliation(s)
- Antreas C. Kalli
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
- * E-mail:
| | - Mark S. P. Sansom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
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Kankipati HN, Rubio-Texeira M, Castermans D, Diallinas G, Thevelein JM. Sul1 and Sul2 sulfate transceptors signal to protein kinase A upon exit of sulfur starvation. J Biol Chem 2015; 290:10430-46. [PMID: 25724649 PMCID: PMC4400352 DOI: 10.1074/jbc.m114.629022] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Indexed: 11/24/2022] Open
Abstract
Sulfate is an essential nutrient with pronounced regulatory effects on cellular metabolism and proliferation. Little is known, however, about how sulfate is sensed by cells. Sul1 and Sul2 are sulfate transporters in the yeast Saccharomyces cerevisiae, strongly induced upon sulfur starvation and endocytosed upon the addition of sulfate. We reveal Sul1,2-dependent activation of PKA targets upon sulfate-induced exit from growth arrest after sulfur starvation. We provide two major arguments in favor of Sul1 and Sul2 acting as transceptors for signaling to PKA. First, the sulfate analogue, d-glucosamine 2-sulfate, acted as a non-transported agonist of signaling by Sul1 and Sul2. Second, mutagenesis to Gln of putative H+-binding residues, Glu-427 in Sul1 or Glu-443 in Sul2, abolished transport without affecting signaling. Hence, Sul1,2 can function as pure sulfate sensors. Sul1E427Q and Sul2E443Q are also deficient in sulfate-induced endocytosis, which can therefore be uncoupled from signaling. Overall, our data suggest that transceptors can undergo independent conformational changes, each responsible for triggering different downstream processes. The Sul1 and Sul2 transceptors are the first identified plasma membrane sensors for extracellular sulfate. High affinity transporters induced upon starvation for their substrate may generally act as transceptors during exit from starvation.
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Affiliation(s)
- Harish Nag Kankipati
- From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and
| | - Marta Rubio-Texeira
- From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and
| | - Dries Castermans
- From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and
| | - George Diallinas
- the Faculty of Biology, University of Athens, Panepistimioupolis, Athens 15784, Greece
| | - Johan M Thevelein
- From the Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, the Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium, and
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Functional characterization of NAT/NCS2 proteins of Aspergillus brasiliensis reveals a genuine xanthine-uric acid transporter and an intrinsically misfolded polypeptide. Fungal Genet Biol 2015; 75:56-63. [PMID: 25639910 DOI: 10.1016/j.fgb.2015.01.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 01/04/2015] [Accepted: 01/21/2015] [Indexed: 01/28/2023]
Abstract
The Nucleobase-Ascorbate Transporter (NAT) family includes members in nearly all domains of life. Functionally characterized NAT transporters from bacteria, fungi, plants and mammals are ion-coupled symporters specific for the uptake of purines, pyrimidines and related analogues. The characterized mammalian NATs are specific for the uptake of L-ascorbic acid. In this work we identify in silico a group of fungal putative transporters, named UapD-like proteins, which represent a novel NAT subfamily. To understand the function and specificity of UapD proteins, we cloned and functionally characterized the two Aspergillus brasiliensis NAT members (named AbUapC and AbUapD) by heterologous expression in Aspergillus nidulans. AbUapC represents canonical NATs (UapC or UapA), while AbUapD represents the new subfamily. AbUapC is a high-affinity, high-capacity, H(+)/xanthine-uric acid transporter, which can also recognize other purines with very low affinity. No apparent transport function could be detected for AbUapD. GFP-tagging showed that, unlike AbUapC which is localized in the plasma membrane, AbUapD is ER-retained and degraded in the vacuoles, a characteristic of misfolded proteins. Chimeric UapA/AbUapD molecules are also turned-over in the vacuole, suggesting that UapD includes intrinsic peptidic sequences leading to misfolding. The possible evolutionary implication of such conserved, but inactive proteins is discussed.
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27
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Niopek-Witz S, Deppe J, Lemieux MJ, Möhlmann T. Biochemical characterization and structure–function relationship of two plant NCS2 proteins, the nucleobase transporters NAT3 and NAT12 from Arabidopsis thaliana. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:3025-35. [DOI: 10.1016/j.bbamem.2014.08.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 07/30/2014] [Accepted: 08/09/2014] [Indexed: 11/28/2022]
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Diallinas G. Understanding transporter specificity and the discrete appearance of channel-like gating domains in transporters. Front Pharmacol 2014; 5:207. [PMID: 25309439 PMCID: PMC4162363 DOI: 10.3389/fphar.2014.00207] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 08/22/2014] [Indexed: 12/12/2022] Open
Abstract
Transporters are ubiquitous proteins mediating the translocation of solutes across cell membranes, a biological process involved in nutrition, signaling, neurotransmission, cell communication and drug uptake or efflux. Similarly to enzymes, most transporters have a single substrate binding-site and thus their activity follows Michaelis-Menten kinetics. Substrate binding elicits a series of structural changes, which produce a transporter conformer open toward the side opposite to the one from where the substrate was originally bound. This mechanism, involving alternate outward- and inward-facing transporter conformers, has gained significant support from structural, genetic, biochemical and biophysical approaches. Most transporters are specific for a given substrate or a group of substrates with similar chemical structure, but substrate specificity and/or affinity can vary dramatically, even among members of a transporter family that show high overall amino acid sequence and structural similarity. The current view is that transporter substrate affinity or specificity is determined by a small number of interactions a given solute can make within a specific binding site. However, genetic, biochemical and in silico modeling studies with the purine transporter UapA of the filamentous ascomycete Aspergillus nidulans have challenged this dogma. This review highlights results leading to a novel concept, stating that substrate specificity, but also transport kinetics and transporter turnover, are determined by subtle intramolecular interactions between a major substrate binding site and independent outward- or cytoplasmically-facing gating domains, analogous to those present in channels. This concept is supported by recent structural evidence from several, phylogenetically and functionally distinct transporter families. The significance of this concept is discussed in relationship to the role and potential exploitation of transporters in drug action.
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Sanguinetti M, Amillis S, Pantano S, Scazzocchio C, Ramón A. Modelling and mutational analysis of Aspergillus nidulans UreA, a member of the subfamily of urea/H⁺ transporters in fungi and plants. Open Biol 2014; 4:140070. [PMID: 24966243 PMCID: PMC4077062 DOI: 10.1098/rsob.140070] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 06/03/2014] [Indexed: 01/02/2023] Open
Abstract
We present the first account of the structure-function relationships of a protein of the subfamily of urea/H(+) membrane transporters of fungi and plants, using Aspergillus nidulans UreA as a study model. Based on the crystal structures of the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT) and of the Nucleobase-Cation-Symport-1 benzylhydantoin transporter from Microbacterium liquefaciens (Mhp1), we constructed a three-dimensional model of UreA which, combined with site-directed and classical random mutagenesis, led to the identification of amino acids important for UreA function. Our approach allowed us to suggest roles for these residues in the binding, recognition and translocation of urea, and in the sorting of UreA to the membrane. Residues W82, Y106, A110, T133, N275, D286, Y388, Y437 and S446, located in transmembrane helixes 2, 3, 7 and 11, were found to be involved in the binding, recognition and/or translocation of urea and the sorting of UreA to the membrane. Y106, A110, T133 and Y437 seem to play a role in substrate selectivity, while S446 is necessary for proper sorting of UreA to the membrane. Other amino acids identified by random classical mutagenesis (G99, R141, A163, G168 and P639) may be important for the basic transporter's structure, its proper folding or its correct traffic to the membrane.
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Affiliation(s)
- Manuel Sanguinetti
- Sección Bioquímica, Departamento de Biología Celular y Molecular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Sotiris Amillis
- Faculty of Biology, Department of Botany, University of Athens, Athens, Greece
| | - Sergio Pantano
- Biomolecular Simulations Group, Institut Pasteur de Montevideo, Montevideo, Uruguay
| | - Claudio Scazzocchio
- Sección Bioquímica, Departamento de Biología Celular y Molecular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay Institut de Génétique et Microbiologie, Université Paris-Sud, Orsay, France Department of Microbiology, Imperial College London, London, UK
| | - Ana Ramón
- Sección Bioquímica, Departamento de Biología Celular y Molecular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
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30
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Krypotou E, Lambrinidis G, Evangelidis T, Mikros E, Diallinas G. Modelling, substrate docking and mutational analysis identify residues essential for function and specificity of the major fungal purine transporter AzgA. Mol Microbiol 2014; 93:129-45. [DOI: 10.1111/mmi.12646] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/08/2014] [Indexed: 01/07/2023]
Affiliation(s)
- Emilia Krypotou
- Faculty of Biology; University of Athens; Panepistimiopolis Athens 15784 Greece
| | - George Lambrinidis
- Faculty of Pharmacy; University of Athens; Panepistimiopolis Athens 15771 Greece
| | - Thomas Evangelidis
- Faculty of Pharmacy; University of Athens; Panepistimiopolis Athens 15771 Greece
| | - Emmanuel Mikros
- Faculty of Pharmacy; University of Athens; Panepistimiopolis Athens 15771 Greece
| | - George Diallinas
- Faculty of Biology; University of Athens; Panepistimiopolis Athens 15784 Greece
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31
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Muñoz-Montesino C, Roa FJ, Peña E, González M, Sotomayor K, Inostroza E, Muñoz CA, González I, Maldonado M, Soliz C, Reyes AM, Vera JC, Rivas CI. Mitochondrial ascorbic acid transport is mediated by a low-affinity form of the sodium-coupled ascorbic acid transporter-2. Free Radic Biol Med 2014; 70:241-54. [PMID: 24594434 DOI: 10.1016/j.freeradbiomed.2014.02.021] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 02/17/2014] [Accepted: 02/24/2014] [Indexed: 10/25/2022]
Abstract
Despite the fundamental importance of the redox metabolism of mitochondria under normal and pathological conditions, our knowledge regarding the transport of vitamin C across mitochondrial membranes remains far from complete. We report here that human HEK-293 cells express a mitochondrial low-affinity ascorbic acid transporter that molecularly corresponds to SVCT2, a member of the sodium-coupled ascorbic acid transporter family 2. The transporter SVCT1 is absent from HEK-293 cells. Confocal colocalization experiments with anti-SVCT2 and anti-organelle protein markers revealed that most of the SVCT2 immunoreactivity was associated with mitochondria, with minor colocalization at the endoplasmic reticulum and very low immunoreactivity at the plasma membrane. Immunoblotting of proteins extracted from highly purified mitochondrial fractions confirmed that SVCT2 protein was associated with mitochondria, and transport analysis revealed a sigmoidal ascorbic acid concentration curve with an apparent ascorbic acid transport Km of 0.6mM. Use of SVCT2 siRNA for silencing SVCT2 expression produced a major decrease in mitochondrial SVCT2 immunoreactivity, and immunoblotting revealed decreased SVCT2 protein expression by approximately 75%. Most importantly, the decreased protein expression was accompanied by a concomitant decrease in the mitochondrial ascorbic acid transport rate. Further studies using HEK-293 cells overexpressing SVCT2 at the plasma membrane revealed that the altered kinetic properties of mitochondrial SVCT2 are due to the ionic intracellular microenvironment (low in sodium and high in potassium), with potassium acting as a concentration-dependent inhibitor of SVCT2. We discarded the participation of two glucose transporters previously described as mitochondrial dehydroascorbic acid transporters; GLUT1 is absent from mitochondria and GLUT10 is not expressed in HEK-293 cells. Overall, our data indicate that intracellular SVCT2 is localized in mitochondria, is sensitive to an intracellular microenvironment low in sodium and high in potassium, and functions as a low-affinity ascorbic acid transporter. We propose that the mitochondrial localization of SVCT2 is a property shared across cells, tissues, and species.
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Affiliation(s)
- Carola Muñoz-Montesino
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Francisco J Roa
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Eduardo Peña
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Mauricio González
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Kirsty Sotomayor
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Eveling Inostroza
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Carolina A Muñoz
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Iván González
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Mafalda Maldonado
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Carlos Soliz
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Alejandro M Reyes
- Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile
| | - Juan Carlos Vera
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Coralia I Rivas
- Departamento de Fisiopatología, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
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32
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Krypotou E, Diallinas G. Transport assays in filamentous fungi: Kinetic characterization of the UapC purine transporter of Aspergillus nidulans. Fungal Genet Biol 2014; 63:1-8. [DOI: 10.1016/j.fgb.2013.12.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 12/09/2013] [Accepted: 12/10/2013] [Indexed: 10/25/2022]
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Ganai SA, Shanmugam K, Mahadevan V. Energy-optimised pharmacophore approach to identify potential hotspots during inhibition of Class II HDAC isoforms. J Biomol Struct Dyn 2014; 33:374-87. [PMID: 24460542 DOI: 10.1080/07391102.2013.879073] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Histone deacetylases (HDACs) are conjugated enzymes that modulate chromatin architecture by deacetylating lysine residues on the histone tails leading to transcriptional repression. Pharmacological interventions of these enzymes with small molecule inhibitors called Histone deacetylase inhibitors (HDACi) have shown enhanced acetylation of the genome and are hence emerging as potential targets at the clinic. Type-specific inhibition of Class II HDACs has shown enhanced therapeutic benefits against developmental and neurodegenerative disorders. However, the structural identity of class-specific isoforms limits the potential of their inhibitors in precise targeting of their enzymes. Diverse strategies have been implemented to recognise the features in HDAC enzymes which may help in identifying isoform specificity factors. This work attempts a computational approach that combines in silico docking and energy-optimised pharmacophore (E-pharmacophore) mapping of 18 known HDAC inhibitors and has identified structural variations that regulate their interactions against the six Class II HDAC enzymes considered for the study. This combined approach establishes that inhibitors possessing higher number of aromatic rings in different structural regions might function as potent inhibitors, while inhibitors with scarce ring structures might point to compromised potency. This would aid the rationale for chemical optimisation and design of isoform selective HDAC inhibitors with enhanced affinity and therapeutic efficiency.
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Affiliation(s)
- Shabir Ahmad Ganai
- a Centre for Nanotechnology & Advanced Biomaterials (CeNTAB), School of Chemical & Biotechnology , SASTRA University , Thanjavur 613401 , India
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Papakostas K, Botou M, Frillingos S. Functional identification of the hypoxanthine/guanine transporters YjcD and YgfQ and the adenine transporters PurP and YicO of Escherichia coli K-12. J Biol Chem 2013; 288:36827-40. [PMID: 24214977 DOI: 10.1074/jbc.m113.523340] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The evolutionarily broad family nucleobase-cation symporter-2 (NCS2) encompasses transporters that are conserved in binding site architecture but diverse in substrate selectivity. Putative purine transporters of this family fall into one of two homology clusters: COG2233, represented by well studied xanthine and/or uric acid permeases, and COG2252, consisting of transporters for adenine, guanine, and/or hypoxanthine that remain unknown with respect to structure-function relationships. We analyzed the COG2252 genes of Escherichia coli K-12 with homology modeling, functional overexpression, and mutagenesis and showed that they encode high affinity permeases for the uptake of adenine (PurP and YicO) or guanine and hypoxanthine (YjcD and YgfQ). The two pairs of paralogs differ clearly in their substrate and ligand preferences. Of 25 putative inhibitors tested, PurP and YicO recognize with low micromolar affinity N(6)-benzoyladenine, 2,6-diaminopurine, and purine, whereas YjcD and YgfQ recognize 1-methylguanine, 8-azaguanine, 6-thioguanine, and 6-mercaptopurine and do not recognize any of the PurP ligands. Furthermore, the permeases PurP and YjcD were subjected to site-directed mutagenesis at highly conserved sites of transmembrane segments 1, 3, 8, 9, and 10, which have been studied also in COG2233 homologs. Residues irreplaceable for uptake activity or crucial for substrate selectivity were found at positions occupied by similar role amino acids in the Escherichia coli xanthine- and uric acid-transporting homologs (XanQ and UacT, respectively) and predicted to be at or around the binding site. Our results support the contention that the distantly related transporters of COG2233 and COG2252 use topologically similar side chain determinants to dictate their function and the distinct purine selectivity profiles.
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Affiliation(s)
- Konstantinos Papakostas
- From the Laboratory of Biological Chemistry, University of Ioannina Medical School, 45110 Ioannina, Greece
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35
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Västermark Å, Saier MH. Evolutionary relationship between 5+5 and 7+7 inverted repeat folds within the amino acid-polyamine-organocation superfamily. Proteins 2013; 82:336-46. [PMID: 24038584 DOI: 10.1002/prot.24401] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 07/19/2013] [Accepted: 08/15/2013] [Indexed: 01/12/2023]
Abstract
Evidence has been presented that 5+5 TMS and 7+7 TMS inverted repeat fold transporters are members of a single superfamily named the Amino acid-Polyamine-organoCation (APC) superfamily. However, the evolutionary relationship between the 5+5 and the 7+7 topological types has not been established. We have identified a common fold, consisting of a spiny membrane helix/sheet, followed by a U-like structure and a V-like structure that is recurrent between domain duplicated units of 5+5 and 7+7 inverted repeat folds. This fold is found in the following protein structures: AdiC, ApcT, LeuT, Mhp1, BetP, CaiT, and SglT (all 5+5 TMS repeats), as well as UraA and SulP (7+7 TMS repeats). AdiC, LeuT and Mhp1 have two extra TMSs after the second duplicated domain, SglT has four extra C-terminal TMSs, and BetP has two extra TMSs before the first duplicated domain. UraA and SulP on the other hand have two extra TMSs at the N-terminus of each duplicated domain unit. These observations imply that multiple hairpin and domain duplication events occurred during the evolution of the APC superfamily. We suggest that the five TMS architecture was primordial and that families gained two TMSs on either side of this basic structure via dissimilar hairpin duplications either before or after intragenic duplication. Evidence for homology between TMSs 1-2 of AdiC and TMSs 1-2 and 3-4 of UraA suggests that the 7+7 topology arose via an internal duplication of the N-terminal hairpin loop within the five TMS repeat unit followed by duplication of the 7 TMS domain.
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Affiliation(s)
- Åke Västermark
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, 92093-0116
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36
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Allopurinol and xanthine use different translocation mechanisms and trajectories in the fungal UapA transporter. Biochimie 2013; 95:1755-64. [PMID: 23791789 DOI: 10.1016/j.biochi.2013.05.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 05/31/2013] [Indexed: 01/14/2023]
Abstract
In Aspergillus nidulans UapA is a H(+)-driven transporter specific for xanthine, uric acid and several analogues. Here, genetic and physiological evidence is provided showing that allopurinol is a high-affinity, low-capacity, substrate for UapA. Surprisingly however, transport kinetic measurements showed that, uniquely among all recognized UapA substrates, allopurinol is transported by apparent facilitated diffusion and exhibits a paradoxical effect on the transport of physiological substrates. Specifically, excess xanthine or other UapA substrates inhibit allopurinol uptake, as expected, but the presence of excess allopurinol results in a concentration-dependent enhancement of xanthine binding and transport. Flexible docking approaches failed to detect allopurinol binding in the major UapA substrate binding site, which was recently identified by mutational analysis and substrate docking using all other UapA substrates. These results and genetic evidence suggest that the allopurinol translocation pathway is distinct from, but probably overlapping with, that of physiological UapA substrates. Furthermore, although the stimulating effect of allopurinol on xanthine transport could, in principle, be rationalized by a cryptic allopurinol-specific allosteric site, evidence was obtained supporting that accelerated influx of xanthine is triggered through exchange with cytoplasmically accumulated allopurinol. Our results are in line with recently accumulating evidence revealing atypical and complex mechanisms underlying transport systems.
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Cunningham P, Naftalin RJ. Implications of aberrant temperature-sensitive glucose transport via the glucose transporter deficiency mutant (GLUT1DS) T295M for the alternate-access and fixed-site transport models. J Membr Biol 2013; 246:495-511. [PMID: 23740044 DOI: 10.1007/s00232-013-9564-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 05/15/2013] [Indexed: 12/27/2022]
Abstract
In silico glucose docking to the transporter GLUT1 templated to the crystal structure of Escherichia coli XylE, a bacterial homolog of GLUT1-4 (4GBZ.pdb), reveals multiple docking sites. One site in the external vestibule in the exofacial linker between TM7 and -8 is adjacent to a missense T295M and a 4-mer insertion mutation. Glucose docking to the adjacent site is occluded in these mutants. These mutants cause an atypical form of glucose transport deficiency syndrome (GLUT1DS), where transport into the brain is deficient, although unusually transport into erythrocytes at 4 °C appears normal. A model in which glucose traverses the transporter via a network of saturable fixed sites simulates the temperature sensitivity of normal and mutant glucose influx and the mutation-dependent alterations of influx and efflux asymmetry when expressed in Xenopus oocytes at 37 °C. The explanation for the temperature sensitivity is that at 4 °C glucose influx between the external and internal vestibules is slow and causes glucose to accumulate in the external vestibule. This retards net glucose uptake from the external solution via two parallel sites into the external vestibule, consequently masking any transport defect at either one of these sites. At 37 °C glucose transit between the external and internal vestibules is rapid, with no significant glucose buildup in the external vestibule, and thereby unmasks any transport defect at one of the parallel input sites. Monitoring glucose transport in patients' erythrocytes at higher temperatures may improve the diagnostic accuracy of the functional test of GLUT1DS.
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Affiliation(s)
- Philip Cunningham
- Bioinformatics Division, School of Medicine, King's College London, Franklin-Wilkins Building, Waterloo Campus, London SE1 9HN, UK
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38
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Bürzle M, Suzuki Y, Ackermann D, Miyazaki H, Maeda N, Clémençon B, Burrier R, Hediger MA. The sodium-dependent ascorbic acid transporter family SLC23. Mol Aspects Med 2013; 34:436-54. [PMID: 23506882 DOI: 10.1016/j.mam.2012.12.002] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Accepted: 11/16/2012] [Indexed: 12/31/2022]
Affiliation(s)
- Marc Bürzle
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
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