1
|
Marín-Quílez A, Di Buduo CA, Benito R, Balduini A, Rivera J, Bastida JM. GALE variants associated with syndromic manifestations, macrothrombocytopenia, bleeding, and platelet dysfunction. Platelets 2023; 34:2176699. [PMID: 36846897 DOI: 10.1080/09537104.2023.2176699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Abstract
GALE gene encodes the uridine diphosphate [UDP]-galactose-4-epimerase, which catalyzes the bidirectional interconversion of UDP-glucose to UDP-galactose, and UDP-N-acetyl-glucosamine to UDP-N-acetyl-galactosamine. In that way, GALE balances, through reversible epimerization, the pool of four sugars that are essential during the biosynthesis of glycoproteins and glycolipids. GALE-related disorder presents an autosomal recessive inheritance pattern, and it is commonly associated with galactosemia. Peripheral galactosemia generally associates with non-generalized forms or even asymptomatic presentations, while classical galactosemia may be related to complications such as learning difficulties, developmental delay, cardiac failure, or dysmorphic features. Recently, GALE variants have been related to severe thrombocytopenia, pancytopenia, and in one patient, to myelodysplastic syndrome.
Collapse
Affiliation(s)
- Ana Marín-Quílez
- IBSAL, CIC, IBMCC, Universidad de Salamanca-CSIC, Salamanca, Spain.,Servicio de Hematología y Oncología Médica, Hospital Universitario Morales Meseguer, Centro Regional de Hemodonación, Universidad de Murcia, IMIB-Pascual Parrilla, Murcia, Spain
| | | | - Rocío Benito
- IBSAL, CIC, IBMCC, Universidad de Salamanca-CSIC, Salamanca, Spain
| | - Alessandra Balduini
- Department of Molecular Medicine, University of Pavia, Pavia, Italy.,Department of Biomedical Engineering, Tufts University, Medford, MA, USA
| | - José Rivera
- Servicio de Hematología y Oncología Médica, Hospital Universitario Morales Meseguer, Centro Regional de Hemodonación, Universidad de Murcia, IMIB-Pascual Parrilla, Murcia, Spain
| | - Jose Maria Bastida
- Department of Hematology, Complejo Asistencial Universitario de Salamanca (CAUSA), Instituto de Investigación Biomédica de Salamanca (IBSAL), Universidad de Salamanca (USAL), Salamanca, Spain
| |
Collapse
|
2
|
Meyer-Schuman R, Marte S, Smith TJ, Feely SME, Kennerson M, Nicholson G, Shy ME, Koutmou KS, Antonellis A. A humanized yeast model reveals dominant-negative properties of neuropathy-associated alanyl-tRNA synthetase mutations. Hum Mol Genet 2023; 32:2177-2191. [PMID: 37010095 PMCID: PMC10281750 DOI: 10.1093/hmg/ddad054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 03/29/2023] [Accepted: 03/30/2023] [Indexed: 04/04/2023] Open
Abstract
Aminoacyl-tRNA synthetases (ARSs) are essential enzymes that ligate tRNA molecules to cognate amino acids. Heterozygosity for missense variants or small in-frame deletions in six ARS genes causes dominant axonal peripheral neuropathy. These pathogenic variants reduce enzyme activity without significantly decreasing protein levels and reside in genes encoding homo-dimeric enzymes. These observations raise the possibility that neuropathy-associated ARS variants exert a dominant-negative effect, reducing overall ARS activity below a threshold required for peripheral nerve function. To test such variants for dominant-negative properties, we developed a humanized yeast assay to co-express pathogenic human alanyl-tRNA synthetase (AARS1) mutations with wild-type human AARS1. We show that multiple loss-of-function AARS1 mutations impair yeast growth through an interaction with wild-type AARS1, but that reducing this interaction rescues yeast growth. This suggests that neuropathy-associated AARS1 variants exert a dominant-negative effect, which supports a common, loss-of-function mechanism for ARS-mediated dominant peripheral neuropathy.
Collapse
Affiliation(s)
- Rebecca Meyer-Schuman
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Sheila Marte
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Tyler J Smith
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
| | - Shawna M E Feely
- Department of Neurology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Marina Kennerson
- Northcott Neuroscience Laboratory, ANZAC Research Institute, Sydney, NSW 2139, Australia
- Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia
- Molecular Medicine Laboratory, Concord General Repatriation Hospital, Sydney, NSW 2139, Australia
| | - Garth Nicholson
- Northcott Neuroscience Laboratory, ANZAC Research Institute, Sydney, NSW 2139, Australia
- Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia
- Molecular Medicine Laboratory, Concord General Repatriation Hospital, Sydney, NSW 2139, Australia
| | - Mike E Shy
- Department of Neurology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Kristin S Koutmou
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
| | - Anthony Antonellis
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109, USA
- Department of Neurology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| |
Collapse
|
3
|
Kumar SU, Sankar S, Kumar DT, Younes S, Younes N, Siva R, Doss CGP, Zayed H. Molecular dynamics, residue network analysis, and cross-correlation matrix to characterize the deleterious missense mutations in GALE causing galactosemia III. Cell Biochem Biophys 2021; 79:201-219. [PMID: 33555556 DOI: 10.1007/s12013-020-00960-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/28/2020] [Indexed: 01/17/2023]
Abstract
Epimerase-deficiency galactosemia (EDG) is caused by mutations in the UDP-galactose 4'-epimerase enzyme, encoded by gene GALE. Catalyzing the last reaction in the Leloir pathway, UDP-galactose-4-epimerase catalyzes the interconversion of UDP-galactose and UDP-glucose. This study aimed to use in-depth computational strategies to prioritize the pathogenic missense mutations in GALE protein and investigate the systemic behavior, conformational spaces, atomic motions, and cross-correlation matrix of the GALE protein. We searched four databases (dbSNP, ClinVar, UniProt, and HGMD) and major biological literature databases (PubMed, Science Direct, and Google Scholar), for missense mutations that are associated with EDG patients, our search yielded 190 missense mutations. We applied a systematic computational prediction pipeline, including pathogenicity, stability, biochemical, conservational, protein residue contacts, and structural analysis, to predict the pathogenicity of these mutations. We found three mutations (p.K161N, p.R239W, and p.G302D) with a severe phenotype in patients with EDG that correlated with our computational prediction analysis; thus, they were selected for further structural and simulation analyses to compute the flexibility and stability of the mutant GALE proteins. The three mutants were subjected to molecular dynamics simulation (MDS) with native protein for 200 ns using GROMACS. The MDS demonstrated that these mutations affected the beta-sheets and helical region that are responsible for the catalytic activity; subsequently, affects the stability and flexibility of the mutant proteins along with a decrease and more deviations in compactness when compared to that of a native. Also, three mutations created major variations in the combined atomic motions of the catalytic and C-terminal regions. The network analysis of the residues in the native and three mutant protein structures showed disturbed residue contacts occurred owing to the missense mutations. Our findings help to understand the structural behavior of a protein owing to mutation and are intended to serve as a platform for prioritizing mutations, which could be potential targets for drug discovery and development of targeted therapeutics.
Collapse
Affiliation(s)
- S Udhaya Kumar
- School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, 632014, India
| | - Srivarshini Sankar
- School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, 632014, India
| | - D Thirumal Kumar
- School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, 632014, India
| | - Salma Younes
- Department of Biomedical Sciences, College of Health and Sciences, Qatar University, QU Health, Doha, Qatar
| | - Nadin Younes
- Department of Biomedical Sciences, College of Health and Sciences, Qatar University, QU Health, Doha, Qatar
| | - R Siva
- School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, 632014, India
| | - C George Priya Doss
- School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, 632014, India.
| | - Hatem Zayed
- Department of Biomedical Sciences, College of Health and Sciences, Qatar University, QU Health, Doha, Qatar.
| |
Collapse
|
4
|
Seo A, Gulsuner S, Pierce S, Ben-Harosh M, Shalev H, Walsh T, Krasnov T, Dgany O, Doulatov S, Tamary H, Shimamura A, King MC. Inherited thrombocytopenia associated with mutation of UDP-galactose-4-epimerase (GALE). Hum Mol Genet 2019; 28:133-142. [PMID: 30247636 DOI: 10.1093/hmg/ddy334] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Accepted: 09/07/2018] [Indexed: 12/11/2022] Open
Abstract
Severe thrombocytopenia, characterized by dysplastic megakaryocytes and intracranial bleeding, was diagnosed in six individuals from a consanguineous kindred. Three of the individuals were successfully treated by bone marrow transplant. Whole-exome sequencing and homozygosity mapping of multiple family members, coupled with whole-genome sequencing to reveal shared non-coding variants, revealed one potentially functional variant segregating with thrombocytopenia under a recessive model: GALE p.R51W (c.C151T, NM_001127621). The mutation is extremely rare (allele frequency = 2.5 × 10-05), and the likelihood of the observed co-segregation occurring by chance is 1.2 × 10-06. GALE encodes UDP-galactose-4-epimerase, an enzyme of galactose metabolism and glycosylation responsible for two reversible reactions: interconversion of UDP-galactose with UDP-glucose and interconversion of UDP-N-acetylgalactosamine with UDP-N-acetylglucosamine. The mutation alters an amino acid residue that is conserved from yeast to humans. The variant protein has both significantly lower enzymatic activity for both interconversion reactions and highly significant thermal instability. Proper glycosylation is critical to normal hematopoiesis, in particular to megakaryocyte and platelet development, as reflected in the presence of thrombocytopenia in the context of congenital disorders of glycosylation. Mutations in GALE have not previously been associated with thrombocytopenia. Our results suggest that GALE p.R51W is inadequate for normal glycosylation and thereby may impair megakaryocyte and platelet development. If other mutations in GALE are shown to have similar consequences, this gene may be proven to play a critical role in hematopoiesis.
Collapse
Affiliation(s)
- Aaron Seo
- Department of Genome Sciences, University of Washington, Seattle, WA, USA.,Department of Medicine, Division of Medical Genetics, University of Washington, Seattle, WA, USA
| | - Suleyman Gulsuner
- Department of Genome Sciences, University of Washington, Seattle, WA, USA.,Department of Medicine, Division of Medical Genetics, University of Washington, Seattle, WA, USA
| | - Sarah Pierce
- Department of Genome Sciences, University of Washington, Seattle, WA, USA.,Department of Medicine, Division of Medical Genetics, University of Washington, Seattle, WA, USA
| | - Miri Ben-Harosh
- Department of Pediatric Hematology/Oncology, Soroka Medical Center, Faculty of Medicine, Ben-Gurion University, Beer Sheva, Israel
| | - Hanna Shalev
- Department of Pediatric Hematology/Oncology, Soroka Medical Center, Faculty of Medicine, Ben-Gurion University, Beer Sheva, Israel
| | - Tom Walsh
- Department of Genome Sciences, University of Washington, Seattle, WA, USA.,Department of Medicine, Division of Medical Genetics, University of Washington, Seattle, WA, USA
| | - Tanya Krasnov
- Pediatric Hematology Laboratory, Felsenstein Medical Research Center, Petach Tikva, Israel
| | - Orly Dgany
- Pediatric Hematology Laboratory, Felsenstein Medical Research Center, Petach Tikva, Israel
| | - Sergei Doulatov
- Department of Medicine, Division of Hematology, University of Washington, Seattle, WA, USA
| | - Hannah Tamary
- Pediatric Hematology Laboratory, Felsenstein Medical Research Center, Petach Tikva, Israel.,Hematology Unit, Schneider Children's Medical Center, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Akiko Shimamura
- Department of Pediatric Hematology/Oncology, Boston Children's Hospital, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - Mary-Claire King
- Department of Genome Sciences, University of Washington, Seattle, WA, USA.,Department of Medicine, Division of Medical Genetics, University of Washington, Seattle, WA, USA
| |
Collapse
|
5
|
Wada Y, Kikuchi A, Arai-Ichinoi N, Sakamoto O, Takezawa Y, Iwasawa S, Niihori T, Nyuzuki H, Nakajima Y, Ogawa E, Ishige M, Hirai H, Sasai H, Fujiki R, Shirota M, Funayama R, Yamamoto M, Ito T, Ohara O, Nakayama K, Aoki Y, Koshiba S, Fukao T, Kure S. Biallelic GALM pathogenic variants cause a novel type of galactosemia. Genet Med 2018; 21:1286-1294. [PMID: 30451973 DOI: 10.1038/s41436-018-0340-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Accepted: 10/04/2018] [Indexed: 12/30/2022] Open
Abstract
PURPOSE Galactosemia is caused by metabolic disturbances at various stages of galactose metabolism, including deficiencies in enzymes involved in the Leloir pathway (GALT, GALK1, and GALE). Nevertheless, the etiology of galactosemia has not been identified in a subset of patients. This study aimed to explore the causes of unexplained galactosemia. METHODS Trio-based exome sequencing and/or Sanger sequencing was performed in eight patients with unexplained congenital galactosemia. In vitro enzymatic assays and immunoblot assays were performed to confirm the pathogenicity of the variants. RESULTS The highest blood galactose levels observed in each patient were 17.3-41.9 mg/dl. Bilateral cataracts were observed in two patients. In all eight patients, we identified biallelic variants (p.Arg82*, p.Ile99Leufs*46, p.Gly142Arg, p.Arg267Gly, and p.Trp311*) in the GALM encoding galactose mutarotase, which catalyzes epimerization between β- and α-D-galactose in the first step of the Leloir pathway. GALM enzyme activities were undetectable in lymphoblastoid cell lines established from two patients. Immunoblot analysis showed the absence of the GALM protein in the patients' peripheral blood mononuclear cells. In vitro GALM expression and protein stability assays revealed altered stabilities of the variant GALM proteins. CONCLUSION Biallelic GALM pathogenic variants cause galactosemia, suggesting the existence of type IV galactosemia.
Collapse
Affiliation(s)
- Yoichi Wada
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan
| | - Atsuo Kikuchi
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan.
| | | | - Osamu Sakamoto
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan
| | - Yusuke Takezawa
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan
| | - Shinya Iwasawa
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan
| | - Tetsuya Niihori
- Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan
| | - Hiromi Nyuzuki
- Department of Pediatrics, Niigata University School of Medicine, Niigata, Japan
| | - Yoko Nakajima
- Department of Pediatrics, Fujita Health University School of Medicine, Toyoake, Japan
| | - Erika Ogawa
- Department of Pediatrics and Child Health, Nihon University School of Medicine, Tokyo, Japan
| | - Mika Ishige
- Department of Pediatrics and Child Health, Nihon University School of Medicine, Tokyo, Japan
| | - Hiroki Hirai
- Department of Pediatrics, Ehime Prefectural Central Hospital, Matsuyama, Japan
| | - Hideo Sasai
- Department of Pediatrics, Graduate School of Medicine, Gifu University, Gifu, Japan
| | - Ryoji Fujiki
- Department of Technology Development, Kazusa DNA Research Institute, Kisarazu, Japan
| | - Matsuyuki Shirota
- Division of Interdisciplinary Medical Sciences, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Ryo Funayama
- Division of Cell Proliferation, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Masayuki Yamamoto
- Tohoku Medical Megabank Organization, Tohoku University, Sendai, Japan
| | - Tetsuya Ito
- Department of Pediatrics, Fujita Health University School of Medicine, Toyoake, Japan
| | - Osamu Ohara
- Department of Technology Development, Kazusa DNA Research Institute, Kisarazu, Japan
| | - Keiko Nakayama
- Division of Cell Proliferation, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - Yoko Aoki
- Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan
| | - Seizo Koshiba
- Tohoku Medical Megabank Organization, Tohoku University, Sendai, Japan
| | - Toshiyuki Fukao
- Department of Pediatrics, Graduate School of Medicine, Gifu University, Gifu, Japan
| | - Shigeo Kure
- Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan.,Tohoku Medical Megabank Organization, Tohoku University, Sendai, Japan
| |
Collapse
|
6
|
Timson DJ. The molecular basis of galactosemia — Past, present and future. Gene 2016; 589:133-41. [DOI: 10.1016/j.gene.2015.06.077] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 06/18/2015] [Accepted: 06/29/2015] [Indexed: 12/19/2022]
|
7
|
Paul S, McCorvie TJ, Zschocke J, Timson DJ. Disturbed cofactor binding by a novel mutation in UDP-galactose 4′-epimerase results in a type III galactosemia phenotype at birth. RSC Adv 2016. [DOI: 10.1039/c6ra00306k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The p.A89V variant of UDP-galactose 4′-epimerase (GALE) is less stable and has lower affinity for the NAD+cofactor than the wild-type enzyme.
Collapse
Affiliation(s)
- Stephanie Paul
- School of Biological Sciences
- Queen's University Belfast
- Medical Biology Centre
- Belfast
- UK
| | - Thomas J. McCorvie
- School of Biological Sciences
- Queen's University Belfast
- Medical Biology Centre
- Belfast
- UK
| | - Johannes Zschocke
- Division of Human Genetics
- Innsbruck Medical University
- Innsbruck 6020
- Austria
| | - David J. Timson
- School of Biological Sciences
- Queen's University Belfast
- Medical Biology Centre
- Belfast
- UK
| |
Collapse
|
8
|
Fuchs JE, Muñoz IG, Timson DJ, Pey AL. Experimental and computational evidence on conformational fluctuations as a source of catalytic defects in genetic diseases. RSC Adv 2016. [DOI: 10.1039/c6ra05499d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Catalytic mutants causing inherited type III galactosemia alter active site structural dynamics and shift the native conformational equilibrium towards inactive conformations.
Collapse
Affiliation(s)
- Julian E. Fuchs
- Institute of General, Inorganic and Theoretical Chemistry
- Faculty of Chemistry and Pharmacy
- University of Innsbruck
- Innsbruck
- Austria
| | - Inés G. Muñoz
- Crystallography and Protein Engineering Unit
- Structural Biology and Biocomputing Programme
- Spanish National Cancer Research Centre (CNIO)
- Madrid
- Spain
| | - David J. Timson
- School of Pharmacy and Biomolecular Sciences
- The University of Brighton
- Brighton
- UK
| | - Angel L. Pey
- Department of Physical Chemistry
- Faculty of Sciences
- University of Granada
- Granada
- Spain
| |
Collapse
|
9
|
Brokate-Llanos AM, Monje JM, Murdoch PDS, Muñoz MJ. Developmental defects in a Caenorhabditis elegans model for type III galactosemia. Genetics 2014; 198:1559-69. [PMID: 25298520 PMCID: PMC4256771 DOI: 10.1534/genetics.114.170084] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 10/01/2014] [Indexed: 12/21/2022] Open
Abstract
Type III galactosemia is a metabolic disorder caused by reduced activity of UDP-galactose-4-epimerase, which participates in galactose metabolism and the generation of various UDP-sugar species. We characterized gale-1 in Caenorhabditis elegans and found that a complete loss-of-function mutation is lethal, as has been hypothesized for humans, whereas a nonlethal partial loss-of-function allele causes a variety of developmental abnormalities, likely resulting from the impairment of the glycosylation process. We also observed that gale-1 mutants are hypersensitive to galactose as well as to infections. Interestingly, we found interactions between gale-1 and the unfolded protein response.
Collapse
Affiliation(s)
- Ana M Brokate-Llanos
- Centro Andaluz de Biología del Desarrollo, Consejo Superior de Investigaciones Científicas-Universidad Pablo de Olavide-Junta de Andalucía, 41013 Seville, Spain
| | - José M Monje
- Centro Andaluz de Biología del Desarrollo, Consejo Superior de Investigaciones Científicas-Universidad Pablo de Olavide-Junta de Andalucía, 41013 Seville, Spain
| | - Piedad Del Socorro Murdoch
- Departamento de Bioquímica y Biología Molecular, Facultad de Biología, Universidad de Sevilla, 41012 Seville, Spain
| | - Manuel J Muñoz
- Centro Andaluz de Biología del Desarrollo, Consejo Superior de Investigaciones Científicas-Universidad Pablo de Olavide-Junta de Andalucía, 41013 Seville, Spain
| |
Collapse
|
10
|
Pey AL, Padín-Gonzalez E, Mesa-Torres N, Timson DJ. The metastability of human UDP-galactose 4'-epimerase (GALE) is increased by variants associated with type III galactosemia but decreased by substrate and cofactor binding. Arch Biochem Biophys 2014; 562:103-14. [PMID: 25150110 DOI: 10.1016/j.abb.2014.07.030] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 07/22/2014] [Accepted: 07/23/2014] [Indexed: 01/30/2023]
Abstract
Type III galactosemia is an inherited disease caused by mutations which affect the activity of UDP-galactose 4'-epimerase (GALE). We evaluated the impact of four disease-associated variants (p.N34S, p.G90E, p.V94M and p.K161N) on the conformational stability and dynamics of GALE. Thermal denaturation studies showed that wild-type GALE denatures at temperatures close to physiological, and disease-associated mutations often reduce GALE's thermal stability. This denaturation is under kinetic control and results partly from dimer dissociation. The natural ligands, NAD(+) and UDP-glucose, stabilize GALE. Proteolysis studies showed that the natural ligands and disease-associated variations affect local dynamics in the N-terminal region of GALE. Proteolysis kinetics followed a two-step irreversible model in which the intact protein is cleaved at Ala38 forming a long-lived intermediate in the first step. NAD(+) reduces the rate of the first step, increasing the amount of undigested protein whereas UDP-glucose reduces the rate of the second step, increasing accumulation of the intermediate. Disease-associated variants affect these rates and the amounts of protein in each state. Our results also suggest communication between domains in GALE. We hypothesize that, in vivo, concentrations of natural ligands modulate GALE stability and that it should be possible to discover compounds which mimic the stabilising effects of the natural ligands overcoming mutation-induced destabilization.
Collapse
Affiliation(s)
- Angel L Pey
- Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain.
| | - Esperanza Padín-Gonzalez
- Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain
| | - Noel Mesa-Torres
- Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain
| | - David J Timson
- School of Biological Sciences, Queeńs University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
| |
Collapse
|
11
|
Li Y, Huang X, Harmonay L, Liu Y, Kellogg MD, Fridovich-Keil JL, Berry GT. Liquid chromatography-tandem mass spectrometry enzyme assay for UDP-galactose 4'-epimerase: use of fragment intensity ratio in differentiation of structural isomers. Clin Chem 2014; 60:783-90. [PMID: 24578239 DOI: 10.1373/clinchem.2013.219931] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND Distinction between asymptomatic and potentially clinically significant forms of galactosemia due to UDP-galactose 4'-epimerase (GALE) deficiency requires enzyme measurement in erythrocytes and other cells. We sought to develop a GALE assay using a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method. METHODS The reversible GALE assay was conducted with UDPGal as a substrate. The coeluting reaction product, uridine diphosphate glucose (UDPGlc), and its isomeric substrate, uridine diphosphate galactose (UDPGal), were detected by MS/MS at mass transitions 565 > 280, 565 > 241 and 565 > 403. The UDPGal was enriched in mass transition 565 > 403 compared with UDPGlc, whereas the UDPGlc was enriched in the mass transition 565 > 241 compared with UDPGal. The percentage of UDPGal in the reaction mixture was calculated by use of the ratio of ion intensities of the 2 daughter ions and a fourth-order polynomial calibrator curve. RESULTS The method yielded a mean (SD) GALE activity of 9.8 (2.2) μmol · g(-1) hemoglobin · h(-1) in erythrocyte extracts from 27 controls. The apparent Km of the substrate, UDPGal, was 0.05 mmol/L. The GALE activity ranged from 433 to 993 μmol · g(-1) protein · h(-1) in control lymphoblast extracts. In a blinded test of 22 subjects suspected of GALE deficiency, we identified 6 individuals whose residual activities were below the range of controls, compatible with intermediate GALE deficiency. CONCLUSIONS This assay can be used to distinguish the different forms of GALE deficiency. From an analytical standpoint, differentiating isomers on the basis of fragment intensity ratios should also prove useful for analogous enzymatic studies involving substrates and products that are structural isomers.
Collapse
Affiliation(s)
- Yijun Li
- The Manton Center for Orphan Disease Research, Division of Genetics, Department of Pediatrics
| | | | | | | | | | | | | |
Collapse
|
12
|
Abstract
Galactosemia is an inherited metabolic disease in which galactose is not properly metabolised. There are various theories to explain the molecular pathology, and recent experimental evidence strongly suggests that oxidative stress plays a key role. High galactose diets are damaging to experimental animals and oxidative stress also plays a role in this toxicity which can be alleviated by purple sweet potato colour (PSPC). This plant extract is rich in acetylated anthocyanins which have been shown to quench free radical production. The objective of this Commentary is to advance the hypothesis that PSPC, or compounds therefrom, may be a viable basis for a novel therapy for galactosemia.
Collapse
Affiliation(s)
- David J Timson
- School of Biological Sciences, Medical Biology Centre, Institute for Global Food Security, Queen's University Belfast , Belfast , UK
| |
Collapse
|
13
|
McCorvie TJ, Timson DJ. In silico prediction of the effects of mutations in the human UDP-galactose 4'-epimerase gene: towards a predictive framework for type III galactosemia. Gene 2013; 524:95-104. [PMID: 23644136 DOI: 10.1016/j.gene.2013.04.061] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 03/30/2013] [Accepted: 04/11/2013] [Indexed: 10/26/2022]
Abstract
The enzyme UDP-galactose 4'-epimerase (GALE) catalyses the reversible epimerisation of both UDP-galactose and UDP-N-acetyl-galactosamine. Deficiency of the human enzyme (hGALE) is associated with type III galactosemia. The majority of known mutations in hGALE are missense and private thus making clinical guidance difficult. In this study a bioinformatics approach was employed to analyse the structural effects due to each mutation using both the UDP-glucose and UDP-N-acetylglucosamine bound structures of the wild-type protein. Changes to the enzyme's overall stability, substrate/cofactor binding and propensity to aggregate were also predicted. These predictions were found to be in good agreement with previous in vitro and in vivo studies when data was available and allowed for the differentiation of those mutants that severely impair the enzyme's activity against UDP-galactose. Next this combination of techniques were applied to another twenty-six reported variants from the NCBI dbSNP database that have yet to be studied to predict their effects. This identified p.I14T, p.R184H and p.G302R as likely severely impairing mutations. Although severely impaired mutants were predicted to decrease the protein's stability, overall predicted stability changes only weakly correlated with residual activity against UDP-galactose. This suggests other protein functions such as changes in cofactor and substrate binding may also contribute to the mechanism of impairment. Finally this investigation shows that this combination of different in silico approaches is useful in predicting the effects of mutations and that it could be the basis of an initial prediction of likely clinical severity when new hGALE mutants are discovered.
Collapse
Affiliation(s)
- Thomas J McCorvie
- School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, UK
| | | |
Collapse
|
14
|
Liu Y, Bentler K, Coffee B, Chhay JS, Sarafoglou K, Fridovich-Keil JL. A Case Study of Monozygotic Twins Apparently Homozygous for a Novel Variant of UDP-Galactose 4'-epimerase (GALE) : A Complex Case of Variant GALE. JIMD Rep 2012; 7:89-98. [PMID: 23430501 DOI: 10.1007/8904_2012_153] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Revised: 05/09/2012] [Accepted: 05/11/2012] [Indexed: 01/07/2023] Open
Abstract
Epimerase deficiency galactosemia is an autosomal recessive disorder that results from partial impairment of UDP-galactose 4'-epimerase (GALE), the third enzyme in the Leloir pathway of galactose metabolism. Clinical severity of epimerase deficiency ranges from potentially lethal to apparently benign, likely reflecting the extent of GALE enzyme impairment, among other factors. We report here a case study of monozygotic twins identified by newborn screening with elevated total galactose and normal galactose-1P uridylyltransferase (GALT). Follow-up testing revealed partial impairment of GALE in hemolysates but near-normal activity in lymphoblasts; molecular testing identified a missense substitution, R220W, apparently in the homozygous state. The twins were treated with dietary galactose restriction for the first 18 months of life. During this time, independent testing revealed concurrent diagnoses of Williams Syndrome in both twins, and cytomegalovirus (CMV) infection in one. Expression studies of R220W-hGALE in a null-background strain of Saccharomyces cerevisiae demonstrated a very limited impairment of V (max) for UDP-galactose (UDP-Gal) and K (m) for UDP-N-acetylgalactosamine (UDP-GalNAc), but a galactose challenge in vivo failed to uncover any evidence of impaired Leloir function. Similarly, both twins demonstrated normal hemolysate galactose-1-phosphate (Gal-1P) levels following normalization of their diets at 18 months of age. While these studies cannot rule out a negative consequence from some cryptic GALE impairment in a specific tissue or developmental stage, they suggest that the substitution, R220W, is mild to neutral, so that any GALE impairment in these twins is likely to be peripheral and therefore unlikely to be the cause of the negative outcomes observed.
Collapse
Affiliation(s)
- Ying Liu
- Department of Human Genetics, Emory University, School of Medicine, Room 325.2 Whitehead Building, 615 Michael Street, Atlanta, GA, 30322, USA
| | | | | | | | | | | |
Collapse
|
15
|
Daenzer JMI, Sanders RD, Hang D, Fridovich-Keil JL. UDP-galactose 4'-epimerase activities toward UDP-Gal and UDP-GalNAc play different roles in the development of Drosophila melanogaster. PLoS Genet 2012; 8:e1002721. [PMID: 22654673 PMCID: PMC3359975 DOI: 10.1371/journal.pgen.1002721] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 04/03/2012] [Indexed: 11/19/2022] Open
Abstract
In both humans and Drosophila melanogaster, UDP-galactose 4'-epimerase (GALE) catalyzes two distinct reactions, interconverting UDP-galactose (UDP-gal) and UDP-glucose (UDP-glc) in the final step of the Leloir pathway of galactose metabolism, and also interconverting UDP-N-acetylgalactosamine (UDP-galNAc) and UDP-N-acetylglucosamine (UDP-glcNAc). All four of these UDP-sugars serve as vital substrates for glycosylation in metazoans. Partial loss of GALE in humans results in the spectrum disorder epimerase deficiency galactosemia; partial loss of GALE in Drosophila melanogaster also results in galactose-sensitivity, and complete loss in Drosophila is embryonic lethal. However, whether these outcomes in both humans and flies result from loss of one GALE activity, the other, or both has remained unknown. To address this question, we uncoupled the two activities in a Drosophila model, effectively replacing the endogenous dGALE with prokaryotic transgenes, one of which (Escherichia coli GALE) efficiently interconverts only UDP-gal/UDP-glc, and the other of which (Plesiomonas shigelloides wbgU) efficiently interconverts only UDP-galNAc/UDP-glcNAc. Our results demonstrate that both UDP-gal and UDP-galNAc activities of dGALE are required for Drosophila survival, although distinct roles for each activity can be seen in specific windows of developmental time or in response to a galactose challenge. By extension, these data also suggest that both activities might play distinct and essential roles in humans.
Collapse
Affiliation(s)
- Jennifer M. I. Daenzer
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, United States of America
| | - Rebecca D. Sanders
- Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University, Atlanta, Georgia, United States of America
| | - Darwin Hang
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, United States of America
| | - Judith L. Fridovich-Keil
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
- * E-mail:
| |
Collapse
|
16
|
McCorvie TJ, Liu Y, Frazer A, Gleason TJ, Fridovich-Keil JL, Timson DJ. Altered cofactor binding affects stability and activity of human UDP-galactose 4'-epimerase: implications for type III galactosemia. Biochim Biophys Acta Mol Basis Dis 2012; 1822:1516-26. [PMID: 22613355 DOI: 10.1016/j.bbadis.2012.05.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Revised: 05/08/2012] [Accepted: 05/10/2012] [Indexed: 02/04/2023]
Abstract
Deficiency of UDP-galactose 4'-epimerase is implicated in type III galactosemia. Two variants, p.K161N-hGALE and p.D175N-hGALE, have been previously found in combination with other alleles in patients with a mild form of the disease. Both variants were studied in vivo and in vitro and showed different levels of impairment. p.K161N-hGALE was severely impaired with substantially reduced enzymatic activity, increased thermal stability, reduced cofactor binding and no ability to rescue the galactose-sensitivity of gal10-null yeast. Interestingly p.K161N-hGALE showed less impairment of activity with UDP-N-acetylgalactosamine in comparison to UDP-galactose. Differential scanning fluorimetry revealed that p.K161N-hGALE was more stable than the wild-type protein and only changed stability in the presence of UDP-N-acetylglucosamine and NAD(+). p.D175N-hGALE essentially rescued the galactose-sensitivity of gal10-null yeast, was less stable than the wild-type protein but showed increased stability in the presence of substrates and cofactor. We postulate that p.K161N-hGALE causes its effects by abolishing an important interaction between the protein and the cofactor, whereas p.D175N-hGALE is predicted to remove a stabilizing salt bridge between the ends of two α-helices that contain residues that interact with NAD(+). These results suggest that the cofactor binding is dynamic and that its loss results in significant structural changes that may be important in disease causation.
Collapse
Affiliation(s)
- Thomas J McCorvie
- School of Biological Sciences, Queen's University, Belfast, BT9 7BL, UK
| | | | | | | | | | | |
Collapse
|
17
|
Sen M, Shah B, Rakshit S, Singh V, Padmanabhan B, Ponnusamy M, Pari K, Vishwakarma R, Nandi D, Sadhale PP. UDP-glucose 4, 6-dehydratase activity plays an important role in maintaining cell wall integrity and virulence of Candida albicans. PLoS Pathog 2011; 7:e1002384. [PMID: 22114559 PMCID: PMC3219719 DOI: 10.1371/journal.ppat.1002384] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Accepted: 10/01/2011] [Indexed: 11/18/2022] Open
Abstract
Candida albicans, a human fungal pathogen, undergoes morphogenetic changes that are associated with virulence. We report here that GAL102 in C. albicans encodes a homolog of dTDP-glucose 4,6-dehydratase, an enzyme that affects cell wall properties as well as virulence of many pathogenic bacteria. We found that GAL102 deletion leads to greater sensitivity to antifungal drugs and cell wall destabilizing agents like Calcofluor white and Congo red. The mutant also formed biofilms consisting mainly of hyphal cells that show less turgor. The NMR analysis of cell wall mannans of gal102 deletion strain revealed that a major constituent of mannan is missing and the phosphomannan component known to affect virulence is greatly reduced. We also observed that there was a substantial reduction in the expression of genes involved in biofilm formation but increase in the expression of genes encoding glycosylphosphatidylinositol-anchored proteins in the mutant. These, along with altered mannosylation of cell wall proteins together might be responsible for multiple phenotypes displayed by the mutant. Finally, the mutant was unable to grow in the presence of resident peritoneal macrophages and elicited a weak pro-inflammatory cytokine response in vitro. Similarly, this mutant elicited a poor serum pro-inflammatory cytokine response as judged by IFNγ and TNFα levels and showed reduced virulence in a mouse model of systemic candidiasis. Importantly, an Ala substitution for a conserved Lys residue in the active site motif YXXXK, that abrogates the enzyme activity also showed reduced virulence and increased filamentation similar to the gal102 deletion strain. Since inactivating the enzyme encoded by GAL102 makes the cells sensitive to antifungal drugs and reduces its virulence, it can serve as a potential drug target in combination therapies for C. albicans and related pathogens.
Collapse
Affiliation(s)
- Manimala Sen
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Bhavin Shah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Srabanti Rakshit
- Department of Biochemistry, Indian Institute of Science, Bangalore, India
| | - Vijender Singh
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Bhavna Padmanabhan
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | | | | | | | - Dipankar Nandi
- Department of Biochemistry, Indian Institute of Science, Bangalore, India
| | - Parag P. Sadhale
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
- * E-mail:
| |
Collapse
|
18
|
McCorvie TJ, Wasilenko J, Liu Y, Fridovich-Keil JL, Timson DJ. In vivo and in vitro function of human UDP-galactose 4'-epimerase variants. Biochimie 2011; 93:1747-54. [PMID: 21703329 PMCID: PMC3168732 DOI: 10.1016/j.biochi.2011.06.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Accepted: 06/09/2011] [Indexed: 12/03/2022]
Abstract
Type III galactosemia results from reduced activity of the enzyme UDP-galactose 4'-epimerase. Five disease-associated alleles (G90E, V94M, D103G, N34S and L183P) and three artificial alleles (Y105C, N268D, and M284K) were tested for their ability to alleviate galactose-induced growth arrest in a Saccharomyces cerevisiae strain which lacks endogenous UDP-galactose 4'-epimerase. For all of these alleles, except M284K, the ability to alleviate galactose sensitivity was correlated with the UDP-galactose 4'-epimerase activity detected in cell extracts. The M284K allele, however, was able to substantially alleviate galactose sensitivity, but demonstrated near-zero activity in cell extracts. Recombinant expression of the corresponding protein in Escherichia coli resulted in a protein with reduced enzymatic activity and reduced stability towards denaturants in vitro. This lack of stability may result from the introduction of an unpaired positive charge into a bundle of three α-helices near the surface of the protein. The disparities between the in vivo and in vitro data for M284K-hGALE further suggest that there are additional, stabilising factors present in the cell. Taken together, these results reinforce the need for care in the interpretation of in vitro, enzymatic diagnostic tests for type III galactosemia.
Collapse
Affiliation(s)
- Thomas J. McCorvie
- School of Biological Sciences, Queen’s University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK
| | - Jamie Wasilenko
- Graduate Division of Biological and Biomedical Sciences, Emory University, Atlanta, Georgia, USA
| | - Ying Liu
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA
| | | | - David J. Timson
- School of Biological Sciences, Queen’s University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK
| |
Collapse
|
19
|
Abstract
In most organisms, productive utilization of galactose requires the highly conserved Leloir pathway of galactose metabolism. Yet, if this metabolic pathway is perturbed due to congenital deficiencies of the three associated enzymes, or an overwhelming presence of galactose, this monosaccharide which is abundantly present in milk and many non-dairy foodstuffs, will become highly toxic to humans and animals. Despite more than four decades of intense research, little is known about the molecular mechanisms of galactose toxicity in human patients and animal models. In this contemporary review, we take a unique approach to present an overview of galactose toxicity resulting from the three known congenital disorders of galactose metabolism and from experimental hypergalactosemia. Additionally, we update the reader about research progress on animal models, as well as advances in clinical management and therapies of these disorders.
Collapse
Affiliation(s)
- Kent Lai
- Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.
| | | | | |
Collapse
|
20
|
Bang YL, Nguyen TTT, Trinh TTB, Kim YJ, Song J, Song YH. Functional analysis of mutations in UDP-galactose-4-epimerase (GALE) associated with galactosemia in Korean patients using mammalian GALE-null cells. FEBS J 2009; 276:1952-61. [DOI: 10.1111/j.1742-4658.2009.06922.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
|
21
|
Ho N, Kondakova AN, Knirel YA, Creuzenet C. The biosynthesis and biological role of 6-deoxyheptose in the lipopolysaccharide O-antigen of Yersinia pseudotuberculosis. Mol Microbiol 2008; 68:424-47. [DOI: 10.1111/j.1365-2958.2008.06163.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
|
22
|
Chhay JS, Vargas CA, McCorvie TJ, Fridovich-Keil JL, Timson DJ. Analysis of UDP-galactose 4'-epimerase mutations associated with the intermediate form of type III galactosaemia. J Inherit Metab Dis 2008; 31:108-16. [PMID: 18188677 DOI: 10.1007/s10545-007-0790-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 11/20/2007] [Accepted: 12/04/2007] [Indexed: 11/29/2022]
Abstract
Type III galactosaemia is a hereditary disease caused by reduced activity in the Leloir pathway enzyme, UDP-galactose 4'-epimerase (GALE). Traditionally, the condition has been divided into two forms-a mild, or peripheral, form and a severe, or generalized, form. Recently it has become apparent that there are disease states which are intermediate between these two extremes. Three mutations associated with this intermediate form (S81R, T150M and P293L) were analysed for their kinetic and structural properties in vitro and their effects on galactose-sensitivity of Saccharomyces cerevisiae cells that were deleted for the yeast GALE homologue Gal10p. All three mutations result in impairment of the kinetic parameters (principally the turnover number, k (cat)) compared with the wild-type enzyme. However, the degree of impairment was mild compared with that seen with the mutation (V94M) associated with the generalized form of epimerase deficiency galactosaemia. None of the three mutations tested affected the ability of the protein to dimerize in solution or its susceptibility to limited proteolysis in vitro. Finally, in the yeast model, each of the mutated patient alleles was able to complement the galactose-sensitivity of gal10Delta cells as fully as was the wild-type human allele. Furthermore, there was no difference from control in metabolite profile following galactose exposure for any of these strains. Thus we conclude that the subtle biochemical and metabolic abnormalities detected in patients expressing these GALE alleles likely reflect, at least in part, the reduced enzymatic activity of the encoded GALE proteins.
Collapse
Affiliation(s)
- J S Chhay
- Department of Human Genetics, Emory University School of Medicine, Emory University, Atlanta, Georgia, USA
| | | | | | | | | |
Collapse
|
23
|
Park HD, Park KU, Kim JQ, Shin CH, Yang SW, Lee DH, Song YH, Song J. The molecular basis of UDP-galactose-4-epimerase (GALE) deficiency galactosemia in Korean patients. Genet Med 2006; 7:646-9. [PMID: 16301867 DOI: 10.1097/01.gim.0000194023.27802.2d] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE UDP-galactose-4-epimerase (GALE) deficiency galactosemia is an autosomal recessive disorder and the prevalence of the disease varies among ethnic groups. We aimed to investigate molecular characteristics of the Korean patients with attenuated GALE activity and elevated galactose-1-phosphate levels in blood. METHODS In order to characterize the molecular defects underlying GALE deficiency, the GALE gene of 7 patients showing severe activity decreases was sequenced. PCR-RFLP was performed to confirm the presence of the mutations identified by sequencing. RESULTS Nine mutations were identified: 8 missense mutations (p.A25V, p.R40C, p.D69E, p.E165K, p.R169W, p.R239W, p.G302D, and p.R335H) and one nonsense mutation (p.W336X). Except for p.R335H, all of these mutations are novel. Six patients were compound heterozygotes (p.D69E/p.G302D, p.R40C/p.R169W, p.D69E/p.E165K, p.R239W/p.R335H, p.A25V/p.R169W, and p.G302D/p.R335H) and the remaining patient had only one mutation (p.W336X/not detected). Thirty patients with moderately reduced GALE activity were also tested by PCR-RFLP for the presence of the above mutation, and mutations were detected in 17 of these 30 patients. The frequency of p.G302D (9/30), p.R239W (6/30) and p.R169W (5/30) in our Korean patients with GALE deficiency galactosemia was relatively high. CONCLUSIONS We detected 9 mutations of the GALE gene in Korean galactosemia patients, and confirmed allelic heterogeneity in this disease.
Collapse
Affiliation(s)
- Hyung-Doo Park
- Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Korea
| | | | | | | | | | | | | | | |
Collapse
|
24
|
Wasilenko J, Fridovich-Keil JL. Relationship between UDP-Galactose 4′-Epimerase Activity and Galactose Sensitivity in Yeast. J Biol Chem 2006; 281:8443-9. [PMID: 16452467 DOI: 10.1074/jbc.m600778200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
UDP-galactose 4'-epimerase (GALE) catalyzes the final step of the highly conserved Leloir pathway of galactose metabolism. Loss of GALE in humans results in a variant form of the metabolic disorder, galactosemia. Loss of GALE in yeast results in galactose-dependent growth arrest. Although the role of GALE in galactose metabolism has been recognized for decades, the precise relationship between GALE activity and galactose sensitivity has remained unclear. Here we have explored this relationship by asking the following. 1) Is GALE rate-limiting for galactose metabolism in yeast? 2) What is the relationship between GALE activity and galactose-dependent growth arrest in yeast? 3) What is the relationship between GALE activity and the abnormal accumulation of galactose metabolites in yeast? To answer these questions we engineered a strain of yeast in which GALE was doxycycline-repressible and studied these cells under conditions of intermediate GALE expression. Our results demonstrated a smooth linear relationship between galactose metabolism and GALE activity over a range from 0 to approximately 5% but a steep threshold relationship between growth rate in galactose and GALE activity over the same range. The relationship between abnormal accumulation of metabolites and GALE activity was also linear over the range from 0 to approximately 5%, suggesting that if the abnormal accumulation of metabolites underlies galactose-dependent growth-arrest in GALE-impaired yeast, either the impact of individual metabolites must be synergistic and/or the threshold of sensitivity must be very steep. Together these data reveal important points of similarity and contrast between the roles of GALE and galactose-1-phosphate uridylyltransferase in galactose metabolism in yeast and provide a framework for future studies in mammalian systems.
Collapse
Affiliation(s)
- Jamie Wasilenko
- Graduate Program in Genetics and Molecular Biology, Emory University and Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia 30322, USA
| | | |
Collapse
|
25
|
Abstract
Alpha-D-galactose is metabolized in species ranging from E. coli to mammals predominantly via a series of sequential reactions collectively known as the Leloir pathway. Deficiency of any one of these enzymes in humans results in a form of the inherited metabolic disorder, galactosemia, although the symptoms and severity depend upon the enzyme impaired, and the degree of functional deficiency (Tyfield and Walter, 2002, The Metabolic and Molecular Bases of Inherited Disease. New York: McGraw Hill.). Studies of these enzymes, and the disorders associated with their loss, have led to a much deeper appreciation of the intricate and interwoven levels of regulation that govern their normal function. These insights have further identified likely mediators of outcome severity in patients, and have enabled a rational approach to the development of novel strategies of intervention.
Collapse
Affiliation(s)
- Judith L Fridovich-Keil
- Department of Human Genetics. Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA.
| |
Collapse
|
26
|
Openo KK, Schulz JM, Vargas CA, Orton CS, Epstein MP, Schnur RE, Scaglia F, Berry GT, Gottesman GS, Ficicioglu C, Slonim AE, Schroer RJ, Yu C, Rangel VE, Keenan J, Lamance K, Fridovich-Keil JL. Epimerase-deficiency galactosemia is not a binary condition. Am J Hum Genet 2006; 78:89-102. [PMID: 16385452 PMCID: PMC1380226 DOI: 10.1086/498985] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Accepted: 10/11/2005] [Indexed: 11/03/2022] Open
Abstract
Epimerase-deficiency galactosemia results from the impairment of UDP-galactose 4'-epimerase (GALE), the third enzyme in the Leloir pathway of galactose metabolism. Originally identified as a clinically benign "peripheral" condition with enzyme impairment restricted to circulating blood cells, GALE deficiency was later demonstrated also to exist in a rare but clinically severe "generalized" form, with enzyme impairment affecting a range of tissues. Isolated cases of clinically and/or biochemically intermediate cases of epimerase deficiency have also been reported. We report here studies of 10 patients who, in the neonatal period, received the diagnosis of hemolysate epimerase deficiency. We have characterized these patients with regard to three parameters: (1) GALE activity in transformed lymphoblasts, representing a "nonperipheral" tissue, (2) metabolic sensitivity of those lymphoblasts to galactose challenge in culture, and (3) evidence of normal versus abnormal galactose metabolism in the patients themselves. Our results demonstrate two important points. First, whereas some of the patients studied exhibited near-normal levels of GALE activity in lymphoblasts, consistent with a diagnosis of peripheral epimerase deficiency, many did not. We detected a spectrum of GALE activity levels ranging from 15%-64% of control levels, demonstrating that epimerase deficiency is not a binary condition; it is a continuum disorder. Second, lymphoblasts demonstrating the most severe reduction in GALE activity also demonstrated abnormal metabolite levels in the presence of external galactose and, in some cases, also in the absence of galactose. These abnormalities included elevated galactose-1P, elevated UDP-galactose, and deficient UDP-glucose. Moreover, some of the patients themselves also demonstrated metabolic abnormalities, both on and off galactose-restricted diet. Long-term follow-up studies of these and other patients will be required to elucidate the clinical significance of these biochemical abnormalities and the potential impact of dietary intervention on outcome.
Collapse
Affiliation(s)
- Kimberly K. Openo
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Jenny M. Schulz
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Claudia A. Vargas
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Corey S. Orton
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Michael P. Epstein
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Rhonda E. Schnur
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Fernando Scaglia
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Gerard T. Berry
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Gary S. Gottesman
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Can Ficicioglu
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Alfred E. Slonim
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Richard J. Schroer
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Chunli Yu
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Vanessa E. Rangel
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Jennifer Keenan
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Kerri Lamance
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| | - Judith L. Fridovich-Keil
- Department of Human Genetics, Emory University School of Medicine, Graduate Program in Nutrition Health Sciences, Emory University, and Emory College, Atlanta; Division of Genetics, Department of Pediatrics, Cooper University Hospital/Robert Wood Johnson Medical School, Camden, NJ; Department of Molecular and Human Genetics, Texas Children’s Hospital and Baylor College of Medicine, Houston; Jefferson Medical College and Division of Metabolism, Children’s Hospital of Philadelphia, Philadelphia; SSM Cardinal Glennon Children’s Hospital, St. Louis, MO; Columbia University Medical School, New York; and Greenwood Genetics Center, Greenwood, SC
| |
Collapse
|
27
|
Demendi M, Ishiyama N, Lam J, Berghuis A, Creuzenet C. Towards a better understanding of the substrate specificity of the UDP-N-acetylglucosamine C4 epimerase WbpP. Biochem J 2005; 389:173-80. [PMID: 15752069 PMCID: PMC1184549 DOI: 10.1042/bj20050263] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
WbpP is the only genuine UDP-GlcNAc (UDP-N-acetylglucosamine) C4 epimerase for which both biochemical and structural data are available. This represents a golden opportunity to elucidate the molecular basis for its specificity for N-acetylated substrates. Based on the comparison of the substrate binding site of WbpP with that of other C4 epimerases that convert preferentially non-acetylated substrates, or that are able to convert both acetylated and non-acetylated substrates equally well, specific residues of WbpP were mutated, and the substrate specificity of the mutants was determined by direct biochemical assays and kinetic analyses. Most of the mutations tested were anticipated to trigger a significant switch in substrate specificity, mostly towards a preference for non-acetylated substrates. However, only one of the mutations (A209H) had the expected effect, and most others resulted in enhanced specificity of WbpP for N-acetylated substrates (Q201E, G102K, Q201E/G102K, A209N and S143A). One mutation (S144K) totally abolished enzyme activity. These data indicate that, although all residues targeted in the present study turned out to be important for catalysis, determinants of substrate specificity are not confined to the substrate-binding pocket and that longer range interactions are essential in allowing proper positioning of various ligands in the binding pocket. Hence prediction or engineering of substrate specificity solely based on sequence analysis, or even on modelling of the binding pocket, might lead to incorrect functional assignments.
Collapse
Affiliation(s)
- Melinda Demendi
- *Department of Microbiology and Immunology, University of Western Ontario, London, ON, Canada, N6A 5C1
| | - Noboru Ishiyama
- †Department of Biochemistry, McGill University, Montréal, QC, Canada, H3A 1A4
| | - Joseph S. Lam
- ‡Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Albert M. Berghuis
- †Department of Biochemistry, McGill University, Montréal, QC, Canada, H3A 1A4
- §Department of Microbiology and Immunology, McGill University, Montréal, QC, Canada, H3A 1A4
| | - Carole Creuzenet
- *Department of Microbiology and Immunology, University of Western Ontario, London, ON, Canada, N6A 5C1
- To whom correspondence should be addressed (email )
| |
Collapse
|
28
|
Abstract
UDP-galactose 4-epimerase (GALE, EC 5.1.3.2) catalyses the interconversion of UDP-glucose and UDP-galactose. Point mutations in this enzyme are associated with the genetic disease, type III galactosemia, which exists in two forms - a milder, or peripheral, form and a more severe, or generalized, form. Recombinant wild-type GALE, and nine disease-causing mutations, have all been expressed in, and purified from, Escherichia coli in soluble, active forms. Two of the mutations (N34S and G319E) display essentially wild-type kinetics. The remainder (G90E, V94M, D103G, L183P, K257R, L313M and R335H) are all impaired in turnover number (k cat) and specificity constant (k cat/Km), with G90E and V94M (which is associated with the generalized form of galactosemia) being the most affected. None of the mutations results in a greater than threefold change in the Michaelis constant (Km). Protein-protein crosslinking suggests that none of the mutants are impaired in homodimer formation. The L183P mutation suffers from severe proteolytic degradation during expression and purification. N34S, G90E and D103G all show increased susceptibility to digestion in limited proteolysis experiments. Therefore, it is suggested that reduced catalytic efficiency and increased proteolytic susceptibility of GALE are causative factors in type III galactosemia. Furthermore, there is an approximate correlation between the severity of these defects in the protein structure and function, and the symptoms observed in patients.
Collapse
Affiliation(s)
- David J Timson
- School of Biology & Biochemistry, Queen's University Belfast, Medical Biology Centre, Belfast, UK.
| |
Collapse
|
29
|
Schulz JM, Ross KL, Malmstrom K, Krieger M, Fridovich-Keil JL. Mediators of galactose sensitivity in UDP-galactose 4'-epimerase-impaired mammalian cells. J Biol Chem 2005; 280:13493-502. [PMID: 15701638 DOI: 10.1074/jbc.m414045200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
UDP-galactose 4'-epimerase (GALE) catalyzes the final step in the Leloir pathway of galactose metabolism, interconverting UDP-galactose and UDP-glucose. Unlike its Escherichia coli counterpart, mammalian GALE also interconverts UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. Considering the key roles played by all four of these UDP-sugars in glycosylation, human GALE therefore not only contributes to the Leloir pathway, but also functions as a gatekeeper overseeing the ratios of important substrate pools required for the synthesis of glycosylated macromolecules. Defects in human GALE result in the disorder epimerase-deficiency galactosemia. To explore the relationship among GALE activity, substrate specificity, metabolic balance, and galactose sensitivity in mammalian cells, we employed a previously described GALE-null line of Chinese hamster ovary cells, ldlD. Using a transfection protocol, we generated ldlD derivative cell lines that expressed different levels of wild-type human GALE or E. coli GALE and compared the phenotypes and metabolic profiles of these lines cultured in the presence versus absence of galactose. We found that GALE-null cells accumulated abnormally high levels of Gal-1-P and UDP-Gal and abnormally low levels of UDP-Glc and UDP-GlcNAc in the presence of galactose and that human GALE expression corrected each of these defects. Comparing the human GALE- and E. coli GALE-expressing cells, we found that although GALE activity toward both substrates was required to restore metabolic balance, UDP-GalNAc activity was not required for cell proliferation in the presence of otherwise cytostatic concentrations of galactose. Finally, we found that uridine supplementation, which essentially corrected UDP-Glc and, to a lesser extent UDP-GlcNAc depletion, enabled ldlD cells to proliferate in the presence of galactose despite the continued accumulation of Gal-1-P and UDP-Gal. These data offer important insights into the mechanism of galactose sensitivity in epimerase-impaired cells and suggest a potential novel therapy for patients with epimerase-deficiency galactosemia.
Collapse
Affiliation(s)
- Jenny M Schulz
- Graduate Program in Nutrition and Health Sciences, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | | | |
Collapse
|
30
|
Ross KL, Davis CN, Fridovich-Keil JL. Differential roles of the Leloir pathway enzymes and metabolites in defining galactose sensitivity in yeast. Mol Genet Metab 2004; 83:103-16. [PMID: 15464425 DOI: 10.1016/j.ymgme.2004.07.005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2004] [Revised: 07/04/2004] [Accepted: 07/07/2004] [Indexed: 11/25/2022]
Abstract
The metabolism of galactose via enzymes of the Leloir pathway: galactokinase, galactose-1-P uridylyltransferase, and UDP galactose-4'-epimerase, is a process that has been conserved from Escherichia coli through humans. Impairment of this pathway in patients results in the disease galactosemia. Despite decades of study, the underlying pathophysiology in galactosemia remains unknown. Here we have defined the functional and metabolic implications of impaired galactose metabolism in yeast, by asking two questions: (1) What is the impact of loss of each of the three Leloir enzymes on the ability of cells to metabolize galactose, and on their sensitivity to galactose, and (2) what is the relationship between gal-1P and galactose-sensitivity in yeast? Our results demonstrate that only transferase-null cells are able to deplete their medium of galactose; deletion of kinase or epimerase halts this process. In contrast, only kinase-null cultures grow well in glycerol/ethanol medium despite the addition of galactose; both transferase and epimerase-null yeast arrest growth under these conditions. Indeed, epimerase-null yeast arrest growth at galactose concentrations 10-fold lower than do their transferase-null counterparts. Secondary deletion of kinase relieves growth arrest in both strains. Finally, rather than a continuous relationship between gal-1P and growth arrest, we observed a threshold level of gal-1P (approximately 10 nmol/mg cell DM) above which both transferase-null and epimerase-null cultures could not grow. These results both confirm and significantly extend prior knowledge of galactose metabolism in yeast, and set the stage for future studies into the mediators and mechanism of Leloir-impaired galactose sensitivity in eukaryotes.
Collapse
Affiliation(s)
- Kerry L Ross
- Department of Human Genetics, Emory University School of Medicine, Emory University, Atlanta, GA 30322, USA
| | | | | |
Collapse
|
31
|
Schulz JM, Watson AL, Sanders R, Ross KL, Thoden JB, Holden HM, Fridovich-Keil JL. Determinants of function and substrate specificity in human UDP-galactose 4'-epimerase. J Biol Chem 2004; 279:32796-803. [PMID: 15175331 DOI: 10.1074/jbc.m405005200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
UDP-galactose 4'-epimerase (GALE) interconverts UDP-galactose and UDP-glucose in the final step of the Leloir pathway. Unlike the Escherichia coli enzyme, human GALE (hGALE) also efficiently interconverts a larger pair of substrates: UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. The basis of this differential substrate specificity has remained obscure. Recently, however, x-ray crystallographic data have both predicted essential active site residues and suggested that differential active site cleft volume may be a key factor in determining GALE substrate selectivity. We report here a direct test of this hypothesis. In brief, we have created four substituted alleles: S132A, Y157F, S132A/Y157F, and C307Y-hGALE. While the first three substitutions were predicted to disrupt catalytic activity, the fourth was predicted to reduce active site cleft volume, thereby limiting entry or rotation of the larger but not the smaller substrate. All four alleles were expressed in a null-background strain of Saccharomyces cerevisiae and characterized in terms of activity with regard to both UDP-galactose and UDP-N-acetylgalactosamine. The S132A/Y157F and C307Y-hGALE proteins were also overexpressed in Pichia pastoris and purified for analysis. In all forms tested, the Y157F, S132A, and Y157F/S132A-hGALE proteins each demonstrated a complete loss of activity with respect to both substrates. In contrast, the C307Y-hGALE demonstrated normal activity with respect to UDP-galactose but complete loss of activity with respect to UDP-N-acetylgalactosamine. Together, these results serve to validate the wild-type hGALE crystal structure and fully support the hypothesis that residue 307 acts as a gatekeeper mediating substrate access to the hGALE active site.
Collapse
Affiliation(s)
- Jenny M Schulz
- Graduate Program in Nutrition and Health Sciences, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | | | | | | | |
Collapse
|
32
|
Abstract
The four essential building blocks of cells are proteins, nucleic acids, lipids, and glycans. Also referred to as carbohydrates, glycans are composed of saccharides that are typically linked to lipids and proteins in the secretory pathway. Glycans are highly abundant and diverse biopolymers, yet their functions have remained relatively obscure. This is changing with the advent of genetic reagents and techniques that in the past decade have uncovered many essential roles of specific glycan linkages in living organisms. Glycans appear to modulate biological processes in the development and function of multiple physiologic systems, in part by regulating protein-protein and cell-cell interactions. Moreover, dysregulation of glycan synthesis represents the etiology for a growing number of human genetic diseases. The study of glycans, known as glycobiology, has entered an era of renaissance that coincides with the acquisition of complete genome sequences for multiple organisms and an increased focus upon how posttranslational modifications to protein contribute to the complexity of events mediating normal and disease physiology. Glycan production and modification comprise an estimated 1% of genes in the mammalian genome. Many of these genes encode enzymes termed glycosyltransferases and glycosidases that reside in the Golgi apparatus where they play the major role in constructing the glycan repertoire that is found at the cell surface and among extracellular compartments. We present a review of the recently established functions of glycan structures in the context of mammalian genetic studies focused upon the mouse and human species. Nothing tends so much to the advancement of knowledge as the application of a new instrument. The native intellectual powers of men in different times are not so much the causes of the different success of their labours, as the peculiar nature of the means and artificial resources in their possession. T. Hager: Force of Nature (1)
Collapse
Affiliation(s)
- John B Lowe
- Department of Pathology and Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109, USA.
| | | |
Collapse
|
33
|
Winans KA, Bertozzi CR. An inhibitor of the human UDP-GlcNAc 4-epimerase identified from a uridine-based library: a strategy to inhibit O-linked glycosylation. CHEMISTRY & BIOLOGY 2002; 9:113-29. [PMID: 11841944 DOI: 10.1016/s1074-5521(02)00093-5] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The biological study of O-linked glycosylation is particularly problematic, as chemical tools to control this modification are lacking. An inhibitor of the UDP-GlcNAc 4-epimerase that synthesizes UDP-GalNAc, the donor initiating O-linked glycosylation, would be a powerful reagent for reversibly inhibiting O-linked glycosylation. We synthesized a 1338 member library of uridine analogs directed to the epimerase by virtue of substrate mimicry. Screening of the library identified an inhibitor with a K(i) value of 11 microM. Tests against related enzymes confirmed the compound's specificity for the UDP-GlcNAc 4-epimerase. Inhibitors of a key step of O-linked glycan biosynthesis can be discovered from a directed library screen. Progeny thereof may be powerful tools for controlling O-linked glycosylation in cells.
Collapse
Affiliation(s)
- Katharine A Winans
- Center for New Directions in Organic Synthesis, Department of Chemistry, University of California, Berkeley 94720, USA
| | | |
Collapse
|
34
|
Henderson JM, Huguenin SM, Cowan TM, Fridovich-Keil JL. A PCR-based method for detecting known mutations in the human UDP galactose-4'-epimerase gene associated with epimerase-deficiency galactosemia. Clin Genet 2001; 60:350-5. [PMID: 11903335 DOI: 10.1034/j.1399-0004.2001.600505.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Epimerase-deficiency galactosemia results from impairment of the human enzyme UDP galactose-4'-epimerase (GALE). We report a rapid, internally controlled PCR-based method for detection of nine naturally occurring point mutations in human GALE associated with epimerase deficiency. These mutations were derived from patients whose clinical presentations ranged from mild to severe; all but one of these mutations have been reported previously. The tests described here work well on both cDNA and genomic samples and require no specialized equipment beyond a thermal cycler and an agarose gel electrophoresis system. Finally, although these tests in no way replace the need for biochemical diagnosis in epimerase-deficiency galactosemia, they do provide the possibility of additional molecular information to support a biochemical diagnosis and facilitate the possibility of more accurate carrier testing, should that option be desired.
Collapse
Affiliation(s)
- J M Henderson
- Graduate Program in Nutrition Health Sciences, Emory University School of Medicine, Atlanta, GA 30322, USA
| | | | | | | |
Collapse
|
35
|
Thoden JB, Wohlers TM, Fridovich-Keil JL, Holden HM. Human UDP-galactose 4-epimerase. Accommodation of UDP-N-acetylglucosamine within the active site. J Biol Chem 2001; 276:15131-6. [PMID: 11279032 DOI: 10.1074/jbc.m100220200] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
UDP-galactose 4-epimerase catalyzes the interconversion of UDP-galactose and UDP-glucose during normal galactose metabolism. One of the key structural features in the proposed reaction mechanism for the enzyme is the rotation of a 4'-ketopyranose intermediate within the active site pocket. Recently, the three-dimensional structure of the human enzyme with bound NADH and UDP-glucose was determined. Unlike that observed for the protein isolated from Escherichia coli, the human enzyme can also turn over UDP-GlcNAc to UDP-GalNAc and vice versa. Here we describe the three-dimensional structure of human epimerase complexed with NADH and UDP-GlcNAc. To accommodate the additional N-acetyl group at the C2 position of the sugar, the side chain of Asn-207 rotates toward the interior of the protein and interacts with Glu-199. Strikingly, in the human enzyme, the structural equivalent of Tyr-299 in the E. coli protein is replaced with a cysteine residue (Cys-307) and the active site volume for the human protein is calculated to be approximately 15% larger than that observed for the bacterial epimerase. This combination of a larger active site cavity and amino acid residue replacement most likely accounts for the inability of the E. coli enzyme to interconvert UDP-GlcNAc and UDP-GalNAc.
Collapse
Affiliation(s)
- J B Thoden
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53705, USA
| | | | | | | |
Collapse
|
36
|
He X, Agnihotri G, Liu Hw HW. Novel enzymatic mechanisms in carbohydrate metabolism. Chem Rev 2000; 100:4615-62. [PMID: 11749360 DOI: 10.1021/cr9902998] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- X He
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, Division of Medicinal Chemistry, College of Pharmacy, and Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712
| | | | | |
Collapse
|
37
|
Wohlers TM, Fridovich-Keil JL. Studies of the V94M-substituted human UDPgalactose-4-epimerase enzyme associated with generalized epimerase-deficiency galactosaemia. J Inherit Metab Dis 2000; 23:713-29. [PMID: 11117433 DOI: 10.1023/a:1005682913784] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Impairment of the human enzyme UDPgalactose 4-epimerase (hGALE) results in epimerase-deficiency galactosaemia, an inborn error of metabolism with variable biochemical presentation and clinical outcomes reported to range from benign to severe. Molecular studies of the hGALE loci from patients with epimerase deficiency reveal significant allelic heterogeneity, raising the possibility that variable genotypes may constitute at least one factor contributing to the biochemical and clinical heterogeneity observed. Previously we have identified a single substitution mutation, V94M, present in the homozygous state in all patients genotyped with the severe, generalized form of epimerase-deficiency galactosaemia. We report here further studies of the V94M-hGALE enzyme, overexpressed and purified from a null-background yeast expression system. Our results demonstrate that the mutant protein is impaired relative to the wild-type enzyme predominantly at the level of Vmax rather than of Km. Studies using UDP-N-acetylgalactosamine as a competitor of UDPgalactose further demonstrate that the Km values for these two substrates vary by less than a factor of 3 for both the wild-type and mutant proteins. Finally, we have explored the impact of the V94M substitution on susceptibility of yeast expressing human GALE to galactose toxicity, including changes in the levels of galactose 1-phosphate (gal-1-P) accumulated in these cells at different times following exposure to galactose. We have observed an inverse correlation between the level of GALE activity expressed in a given culture and the degree of galactose toxicity observed. We have further observed an inverse correlation between the level of GALE activity expressed in a culture and the concentration of gal-1-P accumulated in the cells. These data support the hypothesis that elevated levels of gal-1-P may underlie the observed toxicity. They further raise the intriguing possibility that yeast may provide a valuable model not only for assessing the impact of given patient mutations on hGALE function, but also for exploring the metabolic imbalance resulting from impaired activity of GALE in living cells.
Collapse
Affiliation(s)
- T M Wohlers
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, USA
| | | |
Collapse
|
38
|
Creuzenet C, Belanger M, Wakarchuk WW, Lam JS. Expression, purification, and biochemical characterization of WbpP, a new UDP-GlcNAc C4 epimerase from Pseudomonas aeruginosa serotype O6. J Biol Chem 2000; 275:19060-7. [PMID: 10747995 DOI: 10.1074/jbc.m001171200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
B-band lipopolysaccharide is an important virulence factor of the opportunistic pathogen Pseudomonas aeruginosa. WbpP is an enzyme essential for B-band lipopolysaccharide production in serotype O6. Sequence analysis suggests that it is involved in the formation of N-acetylgalacturonic acid. To test this hypothesis, overexpression and biochemical characterization of WbpP were performed. By using spectrophotometric assays and capillary electrophoresis, we show that WbpP is a UDP-GlcNAc C4 epimerase. The K(m) for UDP-GlcNAc and UDP-GalNAc are 197 and 224 micrometer, respectively. At equilibrium, 70% of UDP-GalNAc is converted to UDP-GlcNAc, whereas the yield of the reverse reaction is only 30%. The enzyme can also catalyze the inter-conversion of non-acetylated substrates, although the efficiency of catalysis is significantly lower. Only 15 and 40% of UDP-Glc and UDP-Gal, respectively, are converted at equilibrium. WbpP contains tightly bound NAD(H) and does not require additional cofactors for activity. It exists as a dimer in its native state. This paper is the first report of expression and characterization of a C4 UDP-GlcNAc epimerase at the biochemical level. Moreover, the characterization of the enzymatic function of WbpP will help clarify ambiguous surface carbohydrate biosynthetic pathways in P. aeruginosa and other organisms where homologues of WbpP exist.
Collapse
Affiliation(s)
- C Creuzenet
- Department of Microbiology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | | | | | | |
Collapse
|
39
|
Tyfield L, Reichardt J, Fridovich-Keil J, Croke DT, Elsas LJ, Strobl W, Kozak L, Coskun T, Novelli G, Okano Y, Zekanowski C, Shin Y, Boleda MD. Classical galactosemia and mutations at the galactose-1-phosphate uridyl transferase (GALT) gene. Hum Mutat 2000; 13:417-30. [PMID: 10408771 DOI: 10.1002/(sici)1098-1004(1999)13:6<417::aid-humu1>3.0.co;2-0] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Classical galactosemia is caused by a deficiency in activity of the enzyme galactose-1-phosphate uridyl transferase (GALT), which, in turn, is caused by mutations at the GALT gene. The disorder exhibits considerable allelic heterogeneity and, at the end of 1998, more than 150 different base changes were recorded in 24 different populations and ethnic groups in 15 countries worldwide. The mutations most frequently cited are Q188R, K285N, S135L, and N314D. Q188R is the most common mutation in European populations or in those predominantly of European descent. Overall, it accounts for 60-70% of mutant chromosomes, but there are significant differences in its relative frequency in individual populations. Individuals homoallelic for Q188R tend to have a severe phenotype and this is in keeping with the virtually complete loss of enzyme activity observed in in vitro expression systems. Globally, K285N is rarer, but in many European populations it can be found on 25-40% of mutant chromosomes. It is invariably associated with a severe phenotype. S135L is found almost exclusively in African Americans. In vitro expression results are discrepant, but some individuals carrying S135L appear to exhibit GALT activity in some tissues. Duarte 1 (or Los Angeles) and Duarte 2 (or Duarte) variants carry the same amino acid substitution, N314D, even though D1 is associated with increased erythrocyte GALT activity and D2 with reduced activity. N314D is in linkage disequilibrium with other base changes that differ on the D1 and D2 alleles. N314D does not impair GALT activity in in vitro expression systems. However, there are differences in the abundance of GALT protein in lymphoblastoid cells lines from D2 and D1 individuals. It is unclear whether the specific molecular changes that distinguish the D1 and D2 alleles account for the different activities. The considerable genetic heterogeneity documented to date undoubtedly contributes to the phenotypic heterogeneity that is observed in galactosemia. The additional effects of nonallelic variation and other constitutional factors on phenotypic variability remain to be elucidated.
Collapse
Affiliation(s)
- L Tyfield
- The Lewis Laboratories, Southmead Hospital, Bristol, England, United Kingdom.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
40
|
Shin YS, Korenke GC, Huppke P, Knerr I, Podskarbi T. UDPgalactose epimerase in lens and fibroblasts: activity expression in patients with cataracts and mental retardation. J Inherit Metab Dis 2000; 23:383-6. [PMID: 10896300 DOI: 10.1023/a:1005699719068] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Y S Shin
- Children's Hospital of University of Munich, Germany.
| | | | | | | | | |
Collapse
|
41
|
Thoden JB, Wohlers TM, Fridovich-Keil JL, Holden HM. Crystallographic evidence for Tyr 157 functioning as the active site base in human UDP-galactose 4-epimerase. Biochemistry 2000; 39:5691-701. [PMID: 10801319 DOI: 10.1021/bi000215l] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
UDP-galactose 4-epimerase catalyzes the interconversion of UDP-glucose and UDP-galactose during normal galactose metabolism. In humans, deficiencies in this enzyme lead to the complex disorder referred to as epimerase-deficiency galactosemia. Here, we describe the high-resolution X-ray crystallographic structures of human epimerase in the resting state (i.e., with bound NAD(+)) and in a ternary complex with bound NADH and UDP-glucose. Those amino acid side chains responsible for anchoring the NAD(+) to the protein include Asp 33, Asn 37, Asp 66, Tyr 157, and Lys 161. The glucosyl group of the substrate is bound to the protein via the side-chain carboxamide groups of Asn 187 and Asn 207. Additionally, O(gamma) of Ser 132 and O(eta) of Tyr 157 lie within 2.4 and 3.1 A, respectively, of the 4'-hydroxyl group of the sugar. Comparison of the polypeptide chains for the resting enzyme and for the protein with bound NADH and UDP-glucose demonstrates that the major conformational changes which occur upon substrate binding are limited primarily to the regions defined by Glu 199 to Asp 240 and Gly 274 to Tyr 308. Additionally, this investigation reveals for the first time that a conserved tyrosine, namely Tyr 157, is in the proper position to interact directly with the 4'-hydroxyl group of the sugar substrate and to thus serve as the active-site base. A low barrier hydrogen bond between the 4'-hydroxyl group of the sugar and O(gamma) of Ser 132 facilitates proton transfer from the sugar 4'-hydroxyl group to O(eta) of Tyr 157.
Collapse
Affiliation(s)
- J B Thoden
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53705, USA
| | | | | | | |
Collapse
|
42
|
Morey NJ, Greene CN, Jinks-Robertson S. Genetic analysis of transcription-associated mutation in Saccharomyces cerevisiae. Genetics 2000; 154:109-20. [PMID: 10628973 PMCID: PMC1460922 DOI: 10.1093/genetics/154.1.109] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
High levels of transcription are associated with elevated mutation rates in yeast, a phenomenon referred to as transcription-associated mutation (TAM). The transcription-associated increase in mutation rates was previously shown to be partially dependent on the Rev3p translesion bypass pathway, thus implicating DNA damage in TAM. In this study, we use reversion of a pGAL-driven lys2DeltaBgl allele to further examine the genetic requirements of TAM. We find that TAM is increased by disruption of the nucleotide excision repair or recombination pathways. In contrast, elimination of base excision repair components has only modest effects on TAM. In addition to the genetic studies, the lys2DeltaBgl reversion spectra of repair-proficient low and high transcription strains were obtained. In the low transcription spectrum, most of the frameshift events correspond to deletions of AT base pairs whereas in the high transcription strain, deletions of GC base pairs predominate. These results are discussed in terms of transcription and its role in DNA damage and repair.
Collapse
Affiliation(s)
- N J Morey
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia 30322, USA
| | | | | |
Collapse
|
43
|
Mehta DV, Kabir A, Bhat PJ. Expression of human inositol monophosphatase suppresses galactose toxicity in Saccharomyces cerevisiae: possible implications in galactosemia. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1454:217-26. [PMID: 10452956 DOI: 10.1016/s0925-4439(99)00037-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A suppressor of galactose toxicity in a gal7 yeast strain (lacking galactose 1-phosphate uridyl transferase) has been isolated from a HeLa cell cDNA library. Analysis of the plasmid clone indicated that the insert has an ORF identical to that of hIMPase (human myo-inositol monophosphatase). The ability of hIMPase to suppress galactose toxicity is sensitive to the presence of Li(+) in the medium. A gal7 yeast strain harboring a plasmid containing cloned hIMPase grows on galactose as a sole carbon source. hIMPase mediated galactose metabolism is dependent on the functionality of GAL1 as well as GAL10 encoded galactokinase and epimerase respectively. These results predicted that the UDP-glucose/galactose pyrophosphorylase mediated pathway may be responsible for the relief of galactose toxicity. Experiments conducted to test this prediction revealed that expression of UGP1 encoded UDP-glucose pyrophosphorylase can indeed overcome the relief of galactose toxicity. Moreover, expression of UGP1 allows a gal7 strain to grow on galactose as a sole carbon source. Unlike the hIMPase mediated relief of galactose toxicity, UGP1 mediated relief of galactose toxicity is lithium insensitive. Based on our results and on the basis of available information on galactose toxicity, we suggest an alternative explanation for the molecular mechanism of galactose toxicity.
Collapse
Affiliation(s)
- D V Mehta
- Laboratory of Molecular Genetics, Biotechnology Centre, Indian Institute of Technology, Powai, Mumbai 400 076, India
| | | | | |
Collapse
|
44
|
Wohlers TM, Christacos NC, Harreman MT, Fridovich-Keil JL. Identification and characterization of a mutation, in the human UDP-galactose-4-epimerase gene, associated with generalized epimerase-deficiency galactosemia. Am J Hum Genet 1999; 64:462-70. [PMID: 9973283 PMCID: PMC1377755 DOI: 10.1086/302263] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Epimerase-deficiency galactosemia results from impairment of the human enzyme UDP-galactose-4-epimerase (hGALE). We and others have identified substitution mutations in the hGALE alleles of patients with the clinically mild, peripheral form of epimerase deficiency. We report here the first identification of an hGALE mutation in a patient with the clinically severe, generalized form of epimerase deficiency. The mutation, V94M, was found on both GALE alleles of this patient. This same mutation also was found in the homozygous state in two additional patients with generalized epimerase deficiency. The specific activity of the V94M-hGALE protein expressed in yeast was severely reduced with regard to UDP-galactose and partially reduced with regard to UDP-N-acetylgalactosamine. In contrast, two GALE-variant proteins associated with peripheral epimerase deficiency, L313M-hGALE and D103G-hGALE, demonstrated near-normal levels of activity with regard to both substrates, but a third allele, G90E-hGALE, demonstrated little, if any, detectable activity, despite near-normal abundance. G90E originally was identified in a heterozygous patient whose other allele remains uncharacterized. Thermal lability and protease-sensitivity studies demonstrated compromised stability in all of the partially active mutant enzymes.
Collapse
Affiliation(s)
- T M Wohlers
- Graduate Program in Genetics and Molecular Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | | | | | | |
Collapse
|
45
|
Alano A, Almashanu S, Chinsky JM, Costeas P, Blitzer MG, Wulfsberg EA, Cowan TM. Molecular characterization of a unique patient with epimerase-deficiency galactosaemia. J Inherit Metab Dis 1998; 21:341-50. [PMID: 9700591 DOI: 10.1023/a:1005342306080] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Inherited deficiencies of UDP-galactose 4-epimerase (GALE) have been associated with two distinct phenotypes. The vast majority of North American patients are clinically asymptomatic, are identified through newborn screening programmes for classical galactosaemia, and are of African-American descent. At least two symptomatic patients have been reported, one Pakistani and the other Asian Muslim, both with severe complications in the neonatal period and subsequent mental retardation. Through newborn screening, we have identified a GALE-deficient patient who is of mixed Pakistani/caucasian ancestry. He was clinically well in the neonatal period on a lactose-containing diet, and biochemical studies, including urine reducing sugars and galactitol, were consistent with a diagnosis of peripheral GALE deficiency. Although early developmental milestones were met normally, he now shows significant developmental delays in both motor and language skills. Mutational analysis revealed this patient to be a compound heterozygote at the GALE locus, with mutations N34S and L183P identified in the patient and confirmed in the parents. This report represents the first characterization of specific mutations in a GALE-deficient patient in conjunction with biochemical and clinical phenotype, and facilitates further studies of the GALE enzyme and its role in the different clinical forms of epimerase-deficiency galactosaemia.
Collapse
Affiliation(s)
- A Alano
- Division of Human Genetics, University of Maryland School of Medicine, Baltimore, USA
| | | | | | | | | | | | | |
Collapse
|
46
|
Petry KG, Reichardt JK. The fundamental importance of human galactose metabolism: lessons from genetics and biochemistry. Trends Genet 1998; 14:98-102. [PMID: 9540406 DOI: 10.1016/s0168-9525(97)01379-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cloning and characterization of all three human galactose-metabolic genes (GALK, GALT and GALE) has led to the identification of a number of mutations which are generally of the missense type in patients with galactosemia, an inborn error of metabolism. The predominance of missense mutations is interesting, considering the general importance of galactose metabolism for cellular energy production and proper modification of glycoproteins and glycolipids. Abnormalities in both of these macromolecules have been described in transferase-deficiency galactosemia, the most common and best-studied form of galactosemia. Thus, the parallel biochemical and molecular genetic analyses of human galactose metabolism are shedding light on this under-appreciated metabolic pathway that is critical for cellular energy production, modification of cellular macromolecules and normal human development.
Collapse
Affiliation(s)
- K G Petry
- Institut François Magendie, INSERM U.394 Neurobiologie intégrative, Université Victor Segalen/Bordeaux 2, France.
| | | |
Collapse
|