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Richard J Reece - One of the best experts on this subject based on the ideXlab platform.
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molecular structure of human Galactokinase implications for type ii galactosemia
Journal of Biological Chemistry, 2005Co-Authors: James B Thoden, Richard J Reece, David J Timson, Hazel M HoldenAbstract:Galactokinase functions in the Leloir pathway for galactose metabolism by catalyzing the MgATP-dependent phosphorylation of the C-1 hydroxyl group of alpha-D-galactose. The enzyme is known to belong to the GHMP superfamily of small molecule kinases and has attracted significant research attention for well over 40 years. Approximately 20 mutations have now been identified in human Galactokinase, which result in the diseased state referred to as Type II galactosemia. Here we report the three-dimensional architecture of human Galactokinase with bound alpha-D-galactose and Mg-AMPPNP. The overall fold of the molecule can be described in terms of two domains with the active site wedged between them. The N-terminal domain is dominated by a six-stranded mixed beta-sheet whereas the C-terminal motif contains six alpha-helices and two layers of anti-parallel beta-sheet. Those residues specifically involved in sugar binding include Arg37, Glu43, His44, Asp46, Gly183, Asp186, and Tyr236. The C-1 hydroxyl group of alpha-D-galactose sits within 3.3 A of the gamma-phosphorus of the nucleotide and 3.4 A of the guanidinium group of Arg37. The carboxylate side chain of Asp186 lies within approximately 3.2 A of the C-2 hydroxyl group of alpha-D-galactose and the guanidinium group of Arg37. Both Arg37 and Asp186 are strictly conserved among both prokaryotic and eukaryotic Galactokinases. In addition to providing molecular insight into the active site geometry of the enzyme, the model also provides a structural framework upon which to more fully understand the consequences of the those mutations known to give rise to Type II galactosemia.
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Galactokinase structure function and role in type ii galactosemia
Cellular and Molecular Life Sciences, 2004Co-Authors: Hazel M Holden, James B Thoden, David J Timson, Richard J ReeceAbstract:The conversion of beta-D-galactose to glucose 1-phosphate is accomplished by the action of four enzymes that constitute the Leloir pathway. Galactokinase catalyzes the second step in this pathway, namely the conversion of alpha-D-galactose to galactose 1-phosphate. The enzyme has attracted significant research attention because of its important metabolic role, the fact that defects in the human enzyme can result in the diseased state referred to as galactosemia, and most recently for its utilization via ‘directed evolution’ to create new natural and unnatural sugar 1-phosphates. Additionally, Galactokinase-like molecules have been shown to act as sensors for the intracellular concentration of galactose and, under suitable conditions, to function as transcriptional regulators. This review focuses on the recent X-ray crystallographic analyses of Galactokinase and places the molecular architecture of this protein in context with the extensive biochemical data that have accumulated over the last 40 years regarding this fascinating small molecule kinase.
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substrate specificity and mechanism from the structure of pyrococcus furiosus Galactokinase
Journal of Molecular Biology, 2004Co-Authors: A Hartley, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, V V Barynin, Daniel De Geus, David J Timson, Richard J ReeceAbstract:Galactokinase (GalK) catalyses the first step of the Leloir pathway of galactose metabolism, the ATP-dependent phosphorylation of galactose to galactose-1-phosphate. In man, defects in galactose metabolism can result in disorders with severe clinical consequences, and deficiencies in Galactokinase have been linked with the development of cataracts within the first few months of life. The crystal structure of GalK from Pyrococcus furiosus in complex with MgADP and galactose has been determined to 2.9 A resolution to provide insights into the substrate specificity and catalytic mechanism of the enzyme. The structure consists of two domains with the active site in a cleft at the domain interface. Inspection of the substrate binding pocket identifies the amino acid residues involved in galactose and nucleotide binding and points to both structural and mechanistic similarities with other enzymes of the GHMP kinase superfamily to which GalK belongs. Comparison of the sequence of the Gal3p inducer protein, which is related to GalK and which forms part of the transcriptional activation of the GAL gene cluster in the yeast Saccharomyces cerevisiae, has led to an understanding of the molecular basis of galactose and nucleotide recognition. Finally, the structure has enabled us to further our understanding on the functional consequences of mutations in human GalK which cause galactosemia.
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Sugar recognition by human Galactokinase
2003Co-Authors: Richard J Reece, David J TimsonAbstract:© 2003 Timson and Reece; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL. Background: Galactokinase catalyses the first committed step of galactose catabolism in which the sugar is phosphorylated at the expense of MgATP. Recent structural studies suggest that the enzyme makes several contacts with galactose – five side chain and two main chain hydrogen bonds. Furthermore, it has been suggested that inhibition of Galactokinase may help sufferers of the genetic disease classical galactosemia which is caused by defects in another enzyme of the pathway galactose-1-phosphate uridyl transferase. Galactokinases from different sources have a range of substrate specificities and a diversity of kinetic mechanisms. Therefore only studies on the human enzyme are likely to be of value in the design of therapeutically useful inhibitors. Results: Using recombinant human Galactokinase expressed in and purified from E. coli we have investigated the sugar specificity of the enzyme and the kinetic consequences of mutating residues in the sugar-binding site in order to improve our understanding of substrate recognition by this enzyme. D-galactose and 2-deoxy-D-galactose are substrates for the enzyme, but N-acetyl-Dgalactosamine
David J Timson - One of the best experts on this subject based on the ideXlab platform.
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galactosemia opportunities for novel therapies
2020Co-Authors: Thomas J Mccorvie, David J TimsonAbstract:Abstract Galactosemia is an inherited metabolic disease affecting enzymes of the Leloir pathway of galactose metabolism. There are four types: type I (galactose 1-phosphate uridylyltransferase; GALT), type II (Galactokinase; GALK1), type III (uridine diphosphate [UDP]-galactose 4’-epimerase; GALE), and type IV (galactose mutarotase; GALM). The range of symptoms is wide, ranging from almost asymptomatic to life-threatening damage to the liver, kidneys, and brain. Severely affected patients suffer cognitive disabilities. Current treatment relies on the restriction of galactose (and its precursors such as lactose) from the diet. This is imperfect and often slows, rather than prevents, the development of symptoms. Potential new treatment approaches include enzyme replacement therapy (ERT), inhibition of Galactokinase, antioxidants, phosphate supplementation, and pharmacological chaperones. ERT has been successfully applied in other diseases, but it is likely that the proteins would need to be delivered to the brain to be fully effective. This would present problems with currently available technologies. Antioxidant therapy and phosphate supplementation would treat downstream effects of the disease and not the fundamental causes. They may be useful in conjunction with galactose restriction but are unlikely to provide a complete solution for the most severely affected patients. Galactokinase inhibition has the most underpinning research with several promising compounds identified. It has yet to be tested in clinical trials. Pharmacological chaperone therapy offers the opportunity to correct protein folding and restore activity. Challenges include development of suitable assays, potential for long-term toxicity of drugs that may be taken for a lifetime, and identifying compounds that work with different disease-associated variants.
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insight into the mechanism of Galactokinase role of a critical glutamate residue and helix coil transitions
Biochimica et Biophysica Acta, 2017Co-Authors: Margaret Mcauley, Meilan Huang, David J TimsonAbstract:Abstract Galactokinase, the enzyme which catalyses the first committed step in the Leloir pathway, has attracted interest due to its potential as a biocatalyst and as a possible drug target in the treatment of type I galactosemia. The mechanism of the enzyme is not fully elucidated. Molecular dynamics (MD) simulations of Galactokinase with the active site residues Arg-37 and Asp-186 altered predicted that two regions (residues 174–179 and 231–240) had different dynamics as a consequence. Interestingly, the same two regions were also affected by alterations in Arg-105, Glu-174 and Arg-228. These three residues were identified as important in catalysis in previous computational studies on human Galactokinase. Alteration of Arg-105 to methionine resulted in a modest reduction in activity with little change in stability. When Arg-228 was changed to methionine, the enzyme's interaction with both ATP and galactose was affected. This variant was significantly less stable than the wild-type protein. Changing Glu-174 to glutamine (but not to aspartate) resulted in no detectable activity and a less stable enzyme. Overall, these combined in silico and in vitro studies demonstrate the importance of a negative charge at position 174 and highlight the critical role of the dynamics in to key regions of the protein. We postulate that these regions may be critical for mediating the enzyme's structure and function.
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molecular structure of human Galactokinase implications for type ii galactosemia
Journal of Biological Chemistry, 2005Co-Authors: James B Thoden, Richard J Reece, David J Timson, Hazel M HoldenAbstract:Galactokinase functions in the Leloir pathway for galactose metabolism by catalyzing the MgATP-dependent phosphorylation of the C-1 hydroxyl group of alpha-D-galactose. The enzyme is known to belong to the GHMP superfamily of small molecule kinases and has attracted significant research attention for well over 40 years. Approximately 20 mutations have now been identified in human Galactokinase, which result in the diseased state referred to as Type II galactosemia. Here we report the three-dimensional architecture of human Galactokinase with bound alpha-D-galactose and Mg-AMPPNP. The overall fold of the molecule can be described in terms of two domains with the active site wedged between them. The N-terminal domain is dominated by a six-stranded mixed beta-sheet whereas the C-terminal motif contains six alpha-helices and two layers of anti-parallel beta-sheet. Those residues specifically involved in sugar binding include Arg37, Glu43, His44, Asp46, Gly183, Asp186, and Tyr236. The C-1 hydroxyl group of alpha-D-galactose sits within 3.3 A of the gamma-phosphorus of the nucleotide and 3.4 A of the guanidinium group of Arg37. The carboxylate side chain of Asp186 lies within approximately 3.2 A of the C-2 hydroxyl group of alpha-D-galactose and the guanidinium group of Arg37. Both Arg37 and Asp186 are strictly conserved among both prokaryotic and eukaryotic Galactokinases. In addition to providing molecular insight into the active site geometry of the enzyme, the model also provides a structural framework upon which to more fully understand the consequences of the those mutations known to give rise to Type II galactosemia.
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Galactokinase structure function and role in type ii galactosemia
Cellular and Molecular Life Sciences, 2004Co-Authors: Hazel M Holden, James B Thoden, David J Timson, Richard J ReeceAbstract:The conversion of beta-D-galactose to glucose 1-phosphate is accomplished by the action of four enzymes that constitute the Leloir pathway. Galactokinase catalyzes the second step in this pathway, namely the conversion of alpha-D-galactose to galactose 1-phosphate. The enzyme has attracted significant research attention because of its important metabolic role, the fact that defects in the human enzyme can result in the diseased state referred to as galactosemia, and most recently for its utilization via ‘directed evolution’ to create new natural and unnatural sugar 1-phosphates. Additionally, Galactokinase-like molecules have been shown to act as sensors for the intracellular concentration of galactose and, under suitable conditions, to function as transcriptional regulators. This review focuses on the recent X-ray crystallographic analyses of Galactokinase and places the molecular architecture of this protein in context with the extensive biochemical data that have accumulated over the last 40 years regarding this fascinating small molecule kinase.
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substrate specificity and mechanism from the structure of pyrococcus furiosus Galactokinase
Journal of Molecular Biology, 2004Co-Authors: A Hartley, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, V V Barynin, Daniel De Geus, David J Timson, Richard J ReeceAbstract:Galactokinase (GalK) catalyses the first step of the Leloir pathway of galactose metabolism, the ATP-dependent phosphorylation of galactose to galactose-1-phosphate. In man, defects in galactose metabolism can result in disorders with severe clinical consequences, and deficiencies in Galactokinase have been linked with the development of cataracts within the first few months of life. The crystal structure of GalK from Pyrococcus furiosus in complex with MgADP and galactose has been determined to 2.9 A resolution to provide insights into the substrate specificity and catalytic mechanism of the enzyme. The structure consists of two domains with the active site in a cleft at the domain interface. Inspection of the substrate binding pocket identifies the amino acid residues involved in galactose and nucleotide binding and points to both structural and mechanistic similarities with other enzymes of the GHMP kinase superfamily to which GalK belongs. Comparison of the sequence of the Gal3p inducer protein, which is related to GalK and which forms part of the transcriptional activation of the GAL gene cluster in the yeast Saccharomyces cerevisiae, has led to an understanding of the molecular basis of galactose and nucleotide recognition. Finally, the structure has enabled us to further our understanding on the functional consequences of mutations in human GalK which cause galactosemia.
Corné H. Verhees - One of the best experts on this subject based on the ideXlab platform.
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substrate specificity and mechanism from the structure of pyrococcus furiosus Galactokinase
Journal of Molecular Biology, 2004Co-Authors: A Hartley, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, V V Barynin, Daniel De Geus, David J Timson, Richard J ReeceAbstract:Galactokinase (GalK) catalyses the first step of the Leloir pathway of galactose metabolism, the ATP-dependent phosphorylation of galactose to galactose-1-phosphate. In man, defects in galactose metabolism can result in disorders with severe clinical consequences, and deficiencies in Galactokinase have been linked with the development of cataracts within the first few months of life. The crystal structure of GalK from Pyrococcus furiosus in complex with MgADP and galactose has been determined to 2.9 A resolution to provide insights into the substrate specificity and catalytic mechanism of the enzyme. The structure consists of two domains with the active site in a cleft at the domain interface. Inspection of the substrate binding pocket identifies the amino acid residues involved in galactose and nucleotide binding and points to both structural and mechanistic similarities with other enzymes of the GHMP kinase superfamily to which GalK belongs. Comparison of the sequence of the Gal3p inducer protein, which is related to GalK and which forms part of the transcriptional activation of the GAL gene cluster in the yeast Saccharomyces cerevisiae, has led to an understanding of the molecular basis of galactose and nucleotide recognition. Finally, the structure has enabled us to further our understanding on the functional consequences of mutations in human GalK which cause galactosemia.
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Cloning, purification, crystallization and preliminary crystallographic analysis of Galactokinase from Pyrococcus furiosus.
Acta crystallographica. Section D Biological crystallography, 2003Co-Authors: D. De Geus, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, Andrew P Hartley, David W. RiceAbstract:Galactokinase catalyses the conversion of galactose to galactose-1-phosphate as the first step in the Leloir pathway, a metabolic route that eventually enables the degradation of galactose via the glycolytic pathway. Galactokinases have been isolated from a wide range of prokaryotic and eukaryotic organisms and the enzyme has been identified as a member of the GHMP kinase (Galactokinase, homoserine kinase, mevalonate kinase and phosphomevalonate kinase) superfamily. Pyrococcus furiosus Galactokinase was cloned, expressed in Escherichia coli, purified and crystallized using the hanging-drop method of vapour diffusion with ammonium sulfate as the precipitant. The crystals belong to the space group C222(1), with more than eight subunits in the asymmetric unit and with approximate unit-cell parameters a = 211.7, b = 355.4, c = 165.5 A, alpha = beta = gamma = 90 degrees. The crystals diffract X-rays to 2.9 A resolution on a synchrotron-radiation source. Determination of the structure will provide insights into the molecular basis of substrate recognition and catalysis of this enzyme, for which no structures are currently available.
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Biochemical adaptations of two sugar kinases from the hyperthermophilic archaeon Pyrococcus furiosus.
Biochemical Journal, 2002Co-Authors: Corné H. Verhees, D.g. Koot, Thijs J. G. Ettema, C. Dijkema, Willem M. De Vos, J. Van Der OostAbstract:The hyperthermophilic archaeon Pyrococcus furiosus possesses a modified Embden-Meyerhof pathway, including an unusual ADP-dependent glucokinase (ADP-GLK) and an ADP-dependent phosphofructokinase. In the present study, we report the characterization of a P. furiosus Galactokinase (GALK) and its comparison with the P. furiosus ADP-GLK. The pyrococcal genes encoding the ADP-GLK and GALK were functionally expressed in Escherichia coli, and the proteins were subsequently purified to homogeneity. Both enzymes are specific kinases with an optimal activity at approx. 90 degrees C. Biochemical characterization of these enzymes confirmed that the ADP-GLK is unable to use ATP as the phosphoryl group donor, but revealed that GALK is ATP-dependent and has an extremely high affinity for ATP. There is a discussion about whether the unusual features of these two classes of kinases might reflect adaptations to a relatively low intracellular ATP concentration in the hyperthermophilic archaeon P. furiosus.
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Biochemical adaptations of two sugar kinases from the hyperthermophilic archaeon Pyrococcus furiosus
Journal of Bacteriology, 2002Co-Authors: Corné H. Verhees, D.g. Koot, Thijs J. G. Ettema, C. Dijkema, De W.m. Vos, Van Der John OostAbstract:The hyperthermophilic archaeon Pyrococcus furiosus possesses a modified Embden-Meyerhof pathway, including an unusual ADP-dependent glucokinase (ADP-GLK) and an ADP-dependent phosphofructokinase. In the present study, we report the characterization of a P. furiosus Galactokinase (GALK) and its comparison with the P. furiosus ADP-GLK. The pyrococcal genes encoding the ADP-GLK and GALK were functionally expressed in Escherichia coli, and the proteins were subsequently purified to homogeneity. Both enzymes are specific kinases with an optimal activity at approx. 90°C. Biochemical characterization of these enzymes confirmed that the ADP-GLK is unable to use ATP as the phosphoryl group donor, but revealed that GALK is ATP-dependent and has an extremely high affinity for ATP. There is a discussion about whether the unusual features of these two classes of kinases might reflect adaptations to a relatively low intracellular ATP concentration in the hyperthermophilic archaeon P. furiosus.
J. Van Der Oost - One of the best experts on this subject based on the ideXlab platform.
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substrate specificity and mechanism from the structure of pyrococcus furiosus Galactokinase
Journal of Molecular Biology, 2004Co-Authors: A Hartley, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, V V Barynin, Daniel De Geus, David J Timson, Richard J ReeceAbstract:Galactokinase (GalK) catalyses the first step of the Leloir pathway of galactose metabolism, the ATP-dependent phosphorylation of galactose to galactose-1-phosphate. In man, defects in galactose metabolism can result in disorders with severe clinical consequences, and deficiencies in Galactokinase have been linked with the development of cataracts within the first few months of life. The crystal structure of GalK from Pyrococcus furiosus in complex with MgADP and galactose has been determined to 2.9 A resolution to provide insights into the substrate specificity and catalytic mechanism of the enzyme. The structure consists of two domains with the active site in a cleft at the domain interface. Inspection of the substrate binding pocket identifies the amino acid residues involved in galactose and nucleotide binding and points to both structural and mechanistic similarities with other enzymes of the GHMP kinase superfamily to which GalK belongs. Comparison of the sequence of the Gal3p inducer protein, which is related to GalK and which forms part of the transcriptional activation of the GAL gene cluster in the yeast Saccharomyces cerevisiae, has led to an understanding of the molecular basis of galactose and nucleotide recognition. Finally, the structure has enabled us to further our understanding on the functional consequences of mutations in human GalK which cause galactosemia.
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Cloning, purification, crystallization and preliminary crystallographic analysis of Galactokinase from Pyrococcus furiosus.
Acta crystallographica. Section D Biological crystallography, 2003Co-Authors: D. De Geus, Svetlana E. Sedelnikova, Steven E. Glynn, Patrick J. Baker, Corné H. Verhees, J. Van Der Oost, Andrew P Hartley, David W. RiceAbstract:Galactokinase catalyses the conversion of galactose to galactose-1-phosphate as the first step in the Leloir pathway, a metabolic route that eventually enables the degradation of galactose via the glycolytic pathway. Galactokinases have been isolated from a wide range of prokaryotic and eukaryotic organisms and the enzyme has been identified as a member of the GHMP kinase (Galactokinase, homoserine kinase, mevalonate kinase and phosphomevalonate kinase) superfamily. Pyrococcus furiosus Galactokinase was cloned, expressed in Escherichia coli, purified and crystallized using the hanging-drop method of vapour diffusion with ammonium sulfate as the precipitant. The crystals belong to the space group C222(1), with more than eight subunits in the asymmetric unit and with approximate unit-cell parameters a = 211.7, b = 355.4, c = 165.5 A, alpha = beta = gamma = 90 degrees. The crystals diffract X-rays to 2.9 A resolution on a synchrotron-radiation source. Determination of the structure will provide insights into the molecular basis of substrate recognition and catalysis of this enzyme, for which no structures are currently available.
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Biochemical adaptations of two sugar kinases from the hyperthermophilic archaeon Pyrococcus furiosus.
Biochemical Journal, 2002Co-Authors: Corné H. Verhees, D.g. Koot, Thijs J. G. Ettema, C. Dijkema, Willem M. De Vos, J. Van Der OostAbstract:The hyperthermophilic archaeon Pyrococcus furiosus possesses a modified Embden-Meyerhof pathway, including an unusual ADP-dependent glucokinase (ADP-GLK) and an ADP-dependent phosphofructokinase. In the present study, we report the characterization of a P. furiosus Galactokinase (GALK) and its comparison with the P. furiosus ADP-GLK. The pyrococcal genes encoding the ADP-GLK and GALK were functionally expressed in Escherichia coli, and the proteins were subsequently purified to homogeneity. Both enzymes are specific kinases with an optimal activity at approx. 90 degrees C. Biochemical characterization of these enzymes confirmed that the ADP-GLK is unable to use ATP as the phosphoryl group donor, but revealed that GALK is ATP-dependent and has an extremely high affinity for ATP. There is a discussion about whether the unusual features of these two classes of kinases might reflect adaptations to a relatively low intracellular ATP concentration in the hyperthermophilic archaeon P. furiosus.
Bernhard Seiboth - One of the best experts on this subject based on the ideXlab platform.
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d-Galactose uptake is nonfunctional in the conidiospores of Aspergillus niger
FEMS microbiology letters, 2012Co-Authors: Erzsebet Fekete, Erzsebet Sandor, Bernhard Seiboth, Christian P Kubicek, Ronald P. De Vries, Patricia A. Vankuyk, Éva Fekete, Benjamin Metz, Levente KaraffaAbstract:The majority of black Aspergilli (Aspergillus section Nigri), including Aspergillus niger, as well as many other Ascomycetes fail to germinate on d-galactose as a sole carbon source. Here, we provide evidence that the ability of A. niger to transport d-galactose is growth stage dependent, being absent in the conidiospores but present in the mycelia. Despite earlier claims, we could identify Galactokinase activity in growing cells and all genes of the Leloir pathway (responsible for channelling d-galactose into the EMP pathway) are well induced on d-galactose (and also on lactose, d-xylose and l-arabinose) in the mycelial stage. Expression of all Leloir pathway genes was also detectable in conidiospores, although galE (encoding a Galactokinase) and galD (encoding a galactose-1-phosphate uridylyl transferase) were expressed poorly. These results suggest that the d-galactose-negative phenotype of A. niger conidiospores may be due to the lack of inducer uptake. Keywords: Aspergillus niger; d-galactose; Leloir pathway; uptake; germination
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induction of the gal pathway and cellulase genes involves no transcriptional inducer function of the Galactokinase in hypocrea jecorina
Journal of Biological Chemistry, 2007Co-Authors: Lukas Hartl, Christian P Kubicek, Bernhard SeibothAbstract:The Saccharomyces cerevisiae Galactokinase ScGal1, a key enzyme for D-galactose metabolism, catalyzes the conversion of D-galactose to D-galactose 1-phosphate, whereas its catalytically inactive paralogue, ScGal3, activates the transcription of the GAL pathway genes. In Kluyveromyces lactis the transcriptional inducer function and the Galactokinase activity are encoded by a single bifunctional KlGal1. Here, we investigated the cellular function of the single Galactokinase GAL1 in the multicellular ascomycete Hypocrea jecorina (=Trichoderma reesei) in the induction of the gal genes and of the Galactokinase-dependent induction of the cellulase genes by lactose (1,4-O-beta-D-galactopyranosyl-D-glucose). A comparison of the transcriptional response of a strain deleted in the gal1 gene (no putative transcriptional inducer and no Galactokinase activity), a strain expressing a catalytically inactive GAL1 version (no Galactokinase activity but a putative inducer function), and a strain expressing the Escherichia coli galK (no putative transcriptional inducer but Galactokinase activity) showed that, in contrast to the two yeasts, both the GAL1 protein and the Galactokinase activity are fully dispensable for induction of the Leloir pathway gene gal7 by D-galactose and that only the Galactokinase activity is required for cellulase induction by lactose. The data document a fundamental difference in the mechanisms by which yeasts and multicellular fungi respond to the presence of D-galactose, showing that the Gal1/Gal3-Gal4-Gal80-dependent regulatory circuit does not operate in multicellular fungi.
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the Galactokinase of hypocrea jecorina is essential for cellulase induction by lactose but dispensable for growth on d galactose
Molecular Microbiology, 2004Co-Authors: Bernhard Seiboth, Erzsebet Fekete, Levente Karaffa, Lukas Hartl, Manuela Pail, Christian P KubicekAbstract:Lactose is the only soluble carbon source which can be used economically for the production of cellulases or heterologous proteins under cellulase expression signals by Hypocrea jecorina (=Trichoderma reesei). Towards an understanding of lactose metabolism and its role in cellulase formation, we have cloned and characterized the gal1 (Galactokinase) gene of H. jecorina, which catalyses the first step in d-galactose catabolism. It exhibits a calculated Mr of 57 kDa, and shows moderate identity (about 40%) to its putative homologues of Saccharomyces cerevisiae and Kluyveromyces lactis. Gal1 is a member of the GHMP family, shows conservation of a Gly/Ser rich region involved in ATP binding and of amino acids (Arg 51, Glu 57, Asp 60, Asp 214, Tyr 270) responsible for galactose binding. A single transcript was formed constitutively during the rapid growth phase on all carbon sources investigated and accumulated to about twice this level during growth on d-galactose, l-arabinose and their corresponding polyols. Deletion of gal1 reduces growth on d-galactose but does only slightly affect growth on lactose. This is the result of the operation of a second pathway for d-galactose catabolism, which involves galactitol as an intermediate, and whose transient concentration is strongly enhanced in the delta-gal1 strain. In this pathway, galactitol is catabolised by the lad1-encoded l-arabinitol-4-dehydrogenase, because a gal1/lad1 double delta-mutant failed to grow on d-galactose. In the delta-gal1 strain, induction of the Leloir pathway gene gal7 (encoding galactose-1-phosphate uridylyltransferase) by d-galactose, but not by l-arabinose, is impaired. Induction of cellulase gene expression by lactose is also impaired in a gal1 deleted strain, whereas their induction by sophorose (the putative cellulose-derived inducer) was shown to be normal, thus demonstrating that Galactokinase is a key enzyme for cellulase induction during growth on lactose, and that induction by lactose and sophorose involves different mechanisms.
