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Knychala MM, dos Santos AA, Kretzer LG, Gelsleichter F, Leandro MJ, Fonseca C, Stambuk BU. Strategies for Efficient Expression of Heterologous Monosaccharide Transporters in Saccharomyces cerevisiae. J Fungi (Basel) 2022; 8:jof8010084. [PMID: 35050024 PMCID: PMC8778384 DOI: 10.3390/jof8010084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/09/2022] [Accepted: 01/12/2022] [Indexed: 02/01/2023] Open
Abstract
In previous work, we developed a Saccharomyces cerevisiae strain (DLG-K1) lacking the main monosaccharide transporters (hxt-null) and displaying high xylose reductase, xylitol dehydrogenase and xylulokinase activities. This strain proved to be a useful chassis strain to study new glucose/xylose transporters, as SsXUT1 from Scheffersomyces stipitis. Proteins with high amino acid sequence similarity (78–80%) to SsXUT1 were identified from Spathaspora passalidarum and Spathaspora arborariae genomes. The characterization of these putative transporter genes (SpXUT1 and SaXUT1, respectively) was performed in the same chassis strain. Surprisingly, the cloned genes could not restore the ability to grow in several monosaccharides tested (including glucose and xylose), but after being grown in maltose, the uptake of 14C-glucose and 14C-xylose was detected. While SsXUT1 lacks lysine residues with high ubiquitinylation potential in its N-terminal domain and displays only one in its C-terminal domain, both SpXUT1 and SaXUT1 transporters have several such residues in their C-terminal domains. A truncated version of SpXUT1 gene, deprived of the respective 3′-end, was cloned in DLG-K1 and allowed growth and fermentation in glucose or xylose. In another approach, two arrestins known to be involved in the ubiquitinylation and endocytosis of sugar transporters (ROD1 and ROG3) were knocked out, but only the rog3 mutant allowed a significant improvement of growth and fermentation in glucose when either of the XUT permeases were expressed. Therefore, for the efficient heterologous expression of monosaccharide (e.g., glucose/xylose) transporters in S. cerevisiae, we propose either the removal of lysines involved in ubiquitinylation and endocytosis or the use of chassis strains hampered in the specific mechanism of membrane protein turnover.
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Affiliation(s)
- Marilia M. Knychala
- Center of Biological Sciences, Department of Biochemistry, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil; (M.M.K.); (A.A.d.S.); (L.G.K.); (F.G.)
- Laboratório Nacional de Energia e Geologia, I.P., Unidade de Bioenergia, Estrada do Paço do Lumiar 22, 1649-038 Lisboa, Portugal; (M.J.L.); (C.F.)
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier, Av. da República, 2780-157 Oeiras, Portugal
| | - Angela A. dos Santos
- Center of Biological Sciences, Department of Biochemistry, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil; (M.M.K.); (A.A.d.S.); (L.G.K.); (F.G.)
| | - Leonardo G. Kretzer
- Center of Biological Sciences, Department of Biochemistry, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil; (M.M.K.); (A.A.d.S.); (L.G.K.); (F.G.)
| | - Fernanda Gelsleichter
- Center of Biological Sciences, Department of Biochemistry, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil; (M.M.K.); (A.A.d.S.); (L.G.K.); (F.G.)
| | - Maria José Leandro
- Laboratório Nacional de Energia e Geologia, I.P., Unidade de Bioenergia, Estrada do Paço do Lumiar 22, 1649-038 Lisboa, Portugal; (M.J.L.); (C.F.)
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier, Av. da República, 2780-157 Oeiras, Portugal
| | - César Fonseca
- Laboratório Nacional de Energia e Geologia, I.P., Unidade de Bioenergia, Estrada do Paço do Lumiar 22, 1649-038 Lisboa, Portugal; (M.J.L.); (C.F.)
- Discovery, R&D, Chr. Hansen A/S, 2970 Hørsholm, Denmark
| | - Boris U. Stambuk
- Center of Biological Sciences, Department of Biochemistry, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil; (M.M.K.); (A.A.d.S.); (L.G.K.); (F.G.)
- Correspondence: ; Tel.: +55-48-3721-4449
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Identification of key residues for efficient glucose transport by the hexose transporter CgHxt4 in high sugar fermentation yeast Candida glycerinogenes. Appl Microbiol Biotechnol 2021; 105:7295-7307. [PMID: 34515842 DOI: 10.1007/s00253-021-11567-6] [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: 03/10/2021] [Revised: 08/03/2021] [Accepted: 09/01/2021] [Indexed: 10/20/2022]
Abstract
Efficient hexose transporters are essential for the development of industrial yeast strains with high fermentation performance. We previously identified a hexose transporter, CgHxt4, with excellent sugar uptake performance at ultra-high glucose concentrations (200 g/L) in the high sugar fermenting yeast C. glycerinogenes. To understand the working mechanism of this transporter, we constructed 87 mutants and examined their glucose uptake performance. The results revealed that five residues (N321, N322, F325, G426, and P427) are essential for the efficient glucose transport of CgHxt4. Subsequently, we focused our analysis on the roles of N321 and P427. Specifically, N321 and P427 are likely to play a role in glucose coordination and conformational flexibility, respectively. Our results help to expand the application potential of this transporter and provide insights into the working mechanism of yeast hexose transporter. KEY POINTS: • Five residues, transmembrane segments 7 and 10, were found to be essential for CgHxt4. • N321 and P427 are likely to play a role in glucose coordination and conformational flexibility, respectively. • Chimeric CgHxt5.4TM7 significantly enhanced the performance of CgHxt5.
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Zhang W, Cao Y, Chen G, Liu W. Identification of the structural determinants for efficient glucose transport via segment swapping between two fungal glucose transporters. RSC Adv 2017. [DOI: 10.1039/c7ra01095h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The N- and C-terminal segments exert a profound effect on the glucose transport capability of Stp1.
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Affiliation(s)
- Weixin Zhang
- State Key Laboratory of Microbial Technology
- School of Life Science
- Shandong University
- Jinan 250100
- P. R. China
| | - Yanli Cao
- State Key Laboratory of Microbial Technology
- School of Life Science
- Shandong University
- Jinan 250100
- P. R. China
| | - Guanjun Chen
- State Key Laboratory of Microbial Technology
- School of Life Science
- Shandong University
- Jinan 250100
- P. R. China
| | - Weifeng Liu
- State Key Laboratory of Microbial Technology
- School of Life Science
- Shandong University
- Jinan 250100
- P. R. China
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4
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Xylose and xylose/glucose co-fermentation by recombinant Saccharomyces cerevisiae strains expressing individual hexose transporters. Enzyme Microb Technol 2014; 63:13-20. [DOI: 10.1016/j.enzmictec.2014.05.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 05/08/2014] [Accepted: 05/09/2014] [Indexed: 01/16/2023]
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Kaur J, Bachhawat AK. Gln-222 in transmembrane domain 4 and Gln-526 in transmembrane domain 9 are critical for substrate recognition in the yeast high affinity glutathione transporter, Hgt1p. J Biol Chem 2009; 284:23872-84. [PMID: 19589778 PMCID: PMC2749159 DOI: 10.1074/jbc.m109.029728] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Revised: 07/02/2009] [Indexed: 11/06/2022] Open
Abstract
Hgt1p, a member of the oligopeptide transporter family, is a high affinity glutathione transporter from the yeast Saccharomyces cerevisiae. We have explored the role of polar or charged residues in the putative transmembrane domains of Hgt1p to obtain insights into the structural features of Hgt1p that govern its substrate specificity. A total of 22 charged and polar residues in the predicted transmembrane domains and other conserved regions were subjected to alanine mutagenesis. Functional characterization of these 22 mutants identified 11 mutants which exhibited significant loss in functional activity. All 11 mutants except T114A had protein expression levels comparable with wild type, and all except E744A were proficient in trafficking to the cell surface. Kinetic analyses revealed differential contributions toward the functional activity of Hgt1p by these residues and identified Asn-124 in transmembrane domain 1 (TMD1), Gln-222 in TMD4, Gln-526 in TMD9, and Glu-544, Arg-554, and Lys-562 in the intracellular loop region 537-568 containing the highly conserved proline-rich motif to be essential for the transport activity of the protein. Furthermore, mutants Q222A and Q526A exhibited a nearly 4- and 8-fold increase in the K(m) for glutathione. Interestingly, although Gln-222 is widely conserved among other functionally characterized oligopeptide transporter family members including those having a different substrate specificity, Gln-526 is present only in Hgt1p and Pgt1, the only two known high affinity glutathione transporters. These results provide the first insights into the substrate recognition residues of a high affinity glutathione transporter and on residues/helices involved in substrate translocation in the structurally uncharacterized oligopeptide transporter family.
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Affiliation(s)
- Jaspreet Kaur
- From the Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India
| | - Anand K. Bachhawat
- From the Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India
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6
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Glucose sensing network in Candida albicans: a sweet spot for fungal morphogenesis. EUKARYOTIC CELL 2009; 8:1314-20. [PMID: 19617394 DOI: 10.1128/ec.00138-09] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Morales JC, Reina JJ, Díaz I, Aviñó A, Nieto PM, Eritja R. Experimental measurement of carbohydrate-aromatic stacking in water by using a dangling-ended DNA model system. Chemistry 2008; 14:7828-35. [PMID: 18637649 DOI: 10.1002/chem.200800335] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Protein-carbohydrate recognition is of fundamental importance for a large number of biological processes; carbohydrate-aromatic stacking is a widespread, but poorly understood, structural motif in this recognition. We describe, for the first time, the measurement of carbohydrate-aromatic interactions from their contribution to the stability of a dangling-ended DNA model system. We observe clear differences in the energetics of the interactions of several monosaccharides with a benzene moiety depending on the number of hydroxy groups, the stereochemistry, and the presence of a methyl group in the pyranose ring. A fucose-benzene pair is the most stabilizing of the studied series (-0.4 Kcal mol(-1)) and this interaction can be placed in the same range as other more studied interactions with aromatic residues of proteins, such as Phe-Phe, Phe-Met, or Phe-His. The noncovalent forces involved seem to be dispersion forces and nonconventional hydrogen bonds, whereas hydrophobic effects do not seem to drive the interaction.
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Affiliation(s)
- Juan C Morales
- Department of Bioorganic Chemistry, Instituto de Investigaciones Químicas, CSIC-Universidad de Sevilla, Sevilla, Spain.
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Kasahara T, Ishiguro M, Kasahara M. Comprehensive Chimeric Analysis of Amino Acid Residues Critical for High Affinity Glucose Transport by Hxt2 of Saccharomyces cerevisiae. J Biol Chem 2004; 279:30274-8. [PMID: 15128737 DOI: 10.1074/jbc.m403762200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chimeras of Hxt2 and Hxt1, high affinity and low affinity glucose transporters, respectively, of Saccharomyces cerevisiae, were previously constructed by random replacement of each of the 12 transmembrane segments (TMs) of Hxt2 with the corresponding region of Hxt1. Characterization of these chimeras revealed that at least TMs 1, 5, 7, and 8 of Hxt2 are required for high affinity transport activity. To determine which amino acid residues in these TMs are important for high affinity glucose transport, we systematically shuffled all of the 20 residues in these regions that differ between Hxt2 and Hxt1. Analysis of 60 independent mutant strains identified as expressing high affinity and high capacity glucose transport activity by selection on glucose-limited agar plates revealed that Leu-201 in TM5 of Hxt2 is most important for such activity and that either Cys-195 or Phe-198 is also required for maximal activity.
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Affiliation(s)
- Toshiko Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo 192-0395, Japan.
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Kasahara T, Kasahara M. Transmembrane segments 1, 5, 7 and 8 are required for high-affinity glucose transport by Saccharomyces cerevisiae Hxt2 transporter. Biochem J 2003; 372:247-52. [PMID: 12603199 PMCID: PMC1223383 DOI: 10.1042/bj20030044] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2003] [Revised: 02/17/2003] [Accepted: 02/25/2003] [Indexed: 11/17/2022]
Abstract
Hxt2 is a high-affinity facilitative glucose transporter of Saccharomyces cerevisiae and belongs to the major facilitator superfamily. Hxt1 shares approximately 70% amino acid identity with Hxt2 in its transmembrane segments (TMs) and inter-TM loops, but transports D-glucose with an affinity about one-tenth of that of Hxt2. To determine which TMs of Hxt2 are important for high-affinity glucose transport, we constructed chimaeras of Hxt2 and Hxt1 by randomly replacing each of the 12 TMs of Hxt2 with the corresponding segment of Hxt1, for a total of 4096 different transporters. Among > 20000 yeast transformants screened, 39 different clones were selected by plate assays of high-affinity glucose-transport activity and sequenced. With only two exceptions, the selected chimaeras contained Hxt2 TMs 1, 5, 7 and 8. We then constructed chimaeras corresponding to all 16 possible combinations of Hxt2 TMs 1, 5, 7 and 8. Only one chimaera, namely that containing all four Hxt2 TMs, exhibited transport activity comparable with that of Hxt2. The K (m) and V (max) values for D-glucose transport, and the substrate specificity of this chimaera were almost identical with those of Hxt2. These results indicate that TMs 1, 5, 7 and 8 are necessary for exhibiting high-affinity glucose-transport activity of Hxt2.
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Affiliation(s)
- Toshiko Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo 192-0395, Japan
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Brown S, Chang JL, Sadee W, Babbitt PC. A semiautomated approach to gene discovery through expressed sequence tag data mining: discovery of new human transporter genes. AAPS PHARMSCI 2003; 5:E1. [PMID: 12713273 PMCID: PMC2751469 DOI: 10.1208/ps050101] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Identification and functional characterization of the genes in the human genome remain a major challenge. A principal source of publicly available information used for this purpose is the National Center for Biotechnology Information database of expressed sequence tags (dbEST), which contains over 4 million human ESTs. To extract the information buried in this data more effectively, we have developed a semiautomated method to mine dbEST for uncharacterized human genes. Starting with a single protein input sequence, a family of related proteins from all species is compiled. This entire family is then used to mine the human EST database for new gene candidates. Evaluation of putative new gene candidates in the context of a family of characterized proteins provides a framework for inference of the structure and function of the new genes. When applied to a test data set of 28 families within the major facilitator superfamily (MFS) of membrane transporters, our protocol found 73 previously characterized human MFS genes and 43 new MFS gene candidates. Development of this approach provided insights into the problems and pitfalls of automated data mining using public databases.
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Affiliation(s)
- Shoshana Brown
- Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, 513 Parnassus St., 94143 San Francisco, CA
| | - Jean l. Chang
- Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, 513 Parnassus St., 94143 San Francisco, CA
- Whitehead Institute/MIT Center for Genome Research, 320 Charles St., 02141 Cambridge, MA
| | - Wolfgang Sadee
- Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, 513 Parnassus St., 94143 San Francisco, CA
- Ohio State University Medical Center, 333 W. 10th Ave., 43210-1239 Columbus, OH
| | - Patricia C. Babbitt
- Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, 513 Parnassus St., 94143 San Francisco, CA
- Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, 94143 San Francisco, CA
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Kasahara M, Maeda M, Hayashi S, Mori Y, Abe T. A missense mutation in the Na(+)/glucose cotransporter gene SGLT1 in a patient with congenital glucose-galactose malabsorption: normal trafficking but inactivation of the mutant protein. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1536:141-7. [PMID: 11406349 DOI: 10.1016/s0925-4439(01)00043-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The Na(+)/glucose cotransporter gene SGLT1 was analyzed in a Japanese patient with congenital glucose-galactose malabsorption. Genomic DNA was used as a template for amplification by the polymerase chain reaction of each of the 15 exons of SGLT1. The amplification products were cloned and sequenced. About half of the exon 5 clones of the patient contained a C-->T transition, resulting in an Arg(135)-->Trp mutation, whereas the remaining clones contained the normal exon 5 sequence. In addition, whereas some exon 12 clones exhibited the normal sequence, others showed a CAgtaggtatcatc-->CAgacc mutation at the splice donor site of intron 12 that may result either in the skipping of exon 12 or in read-through of intron 12. Neither the Arg(135)-->Trp mutant nor either of the possible intron 12 mutant proteins exhibited Na(+)-dependent glucose transport activity when expressed in Xenopus oocytes. Immunocytochemical analysis indicated, however, that the Arg(135)-->Trp mutant was localized to the oocyte plasma membrane. DNA sequence analysis revealed that the missense mutation in exon 5 and the splice site mutation in intron 12 were inherited from the proband's father and mother, respectively. These results indicate that the patient is a compound heterozygote for this disease, and that the Arg(135)-->Trp mutant of SGLT1 undergoes normal trafficking to the plasma membrane but is non-functional.
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Affiliation(s)
- M Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, hachioji, Tokyo, Japan.
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12
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Gonçalves P, Rodrigues de Sousa H, Spencer-Martins I. FSY1, a novel gene encoding a specific fructose/H(+) symporter in the type strain of Saccharomyces carlsbergensis. J Bacteriol 2000; 182:5628-30. [PMID: 10986274 PMCID: PMC111014 DOI: 10.1128/jb.182.19.5628-5630.2000] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2000] [Accepted: 07/18/2000] [Indexed: 11/20/2022] Open
Abstract
A novel gene, FSY1, encoding a permease involved in active fructose uptake by a proton symport mechanism in the type strain of Saccharomyces carlsbergensis has been isolated. Fsy1p is only distantly related to the Hxt proteins that mediate facilitated diffusion of glucose and fructose in Saccharomyces cerevisiae and related species.
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Affiliation(s)
- P Gonçalves
- Centro de Recursos Microbiológicos, Biotechnology Unit, Faculty of Sciences and Technology, New University of Lisbon, 2825-114 Caparica, Portugal
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Kasahara T, Kasahara M. Interaction between the critical aromatic amino acid residues Tyr(352) and Phe(504) in the yeast Gal2 transporter. FEBS Lett 2000; 471:103-7. [PMID: 10760522 DOI: 10.1016/s0014-5793(00)01371-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Three critical aromatic sites have been identified in the yeast galactose transporter Gal2: Tyr(352) at the extracellular boundary of putative transmembrane segment (TM) 7, Tyr(446) in the middle of TM10 and Phe(504) in the middle of TM12. The relationship between these sites was investigated by random mutagenesis of each combination of two of the three residues. Galactose transport-positive clones selected by plate assays encoded Tyr(446) and specific combinations of aromatic residues at sites 352 and 504. Double-site mutants containing aromatic residues at these latter two positions showed either essentially full galactose transport activity (Phe(352)Trp(504) and Trp(352)Trp(504)) or no significant activity (Phe(352)Tyr(504) and Trp(352)Tyr(504)), whereas single-site mutants showed markedly reduced activity. These results are indicative of a specific interaction between sites 352 and 504 of Gal2.
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Affiliation(s)
- T Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo, Japan
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14
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Kasahara T, Kasahara M. Three aromatic amino acid residues critical for galactose transport in yeast Gal2 transporter. J Biol Chem 2000; 275:4422-8. [PMID: 10660614 DOI: 10.1074/jbc.275.6.4422] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tyr(446) in putative transmembrane segment 10 (TM10) of the yeast galactose transporter Gal2 has previously been identified as essential for galactose recognition. In the present study, alignment of the amino acid sequences of 63 sugar transporters or related proteins revealed 14 aromatic sites, including Tyr(446) of Gal2, that are conserved in >75% of these proteins. The importance of the remaining 13 conserved aromatic amino acids was examined individually by random mutagenesis using degenerate primers. Galactose transport-positive clones were identified by plate selection and subjected to DNA sequencing. For those transport-positive clones corresponding to Tyr(352), and Phe(504) mutants, all the amino acid substitutions comprised aromatic residues. The importance of the aromatic residues at these sites was further investigated by replacing them individually with each of the other 19 amino acids and measuring the galactose transport activity of the resulting mutants. Among both Tyr(352) and Phe(504) mutants, the other aromatic amino acids supported galactose transport; no other amino acids conferred high affinity transport activity. Thus, at least three aromatic sites are critical for galactose transport: one at the extracellular boundary of putative TM7 (Tyr(352)), one in the middle of putative TM10 (Tyr(446)), and one in the middle of putative TM12 (Phe(504)).
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Affiliation(s)
- T Kasahara
- Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo 192-0395, Japan
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Abstract
Glucose, the most abundant monosaccharide in nature, is the principal carbon and energy source for nearly all cells. The first, and rate-limiting, step of glucose metabolism is its transport across the plasma membrane. In cells of many organisms glucose ensures its own efficient metabolism by serving as an environmental stimulus that regulates the quantity, types, and activity of glucose transporters, both at the transcriptional and posttranslational levels. This is most apparent in the baker's yeast Saccharomyces cerevisiae, which has 20 genes encoding known or likely glucose transporters, each of which is known or likely to have a different affinity for glucose. The expression and function of most of these HXT genes is regulated by different levels of glucose. This review focuses on the mechanisms S. cerevisiae and a few other fungal species utilize for sensing the level of glucose and transmitting this information to the nucleus to alter HXT gene expression. One mechanism represses transcription of some HXT genes when glucose levels are high and works through the Mig1 transcriptional repressor, whose function is regulated by the Snf1-Snf4 protein kinase and Reg1-Glc7 protein phosphatase. Another pathway induces HXT expression in response to glucose and employs the Rgt1 transcriptional repressor, a ubiquitin ligase protein complex (SCF(Grr1)) that regulates Rgt1 function, and two glucose sensors in the membrane (Snf3 and Rgt2) that bind glucose and generate the intracellular signal to which Rgt1 responds. These two regulatory pathways collaborate with other, less well-understood, pathways to ensure that yeast cells express the glucose transporters best suited for the amount of glucose available.
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Affiliation(s)
- S Ozcan
- Department of Biochemistry, College of Medicine, University of Kentucky, Lexington, Kentucky 40536, USA
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Abstract
Sugar transporters from one group of the major facilitator superfamily of membrane transporters. A conserved common central pore structure lies at the heart of these transporters and diverse functionality is brought about by alterations to this pore or regions associated with it. Recent mutagenesis studies of sugar transporters within the framework of tenable models for the distantly related lactose permease argue that this model is a good paradigm for other members of the major facilitator superfamily.
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Affiliation(s)
- M P Barrett
- Divisions of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
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