Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GALACTOSEMIA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources
PubMed2000

Crystallographic evidence for Tyr 157 functioning as the active site base in human UDP-galactose 4-epimerase.

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.

Binding Sites↗
PubMed2002

Hint, Fhit, and GalT: function, structure, evolution, and mechanism of three branches of the histidine triad superfamily of nucleotide hydrolases and transferases.

HIT (histidine triad) proteins, named for a motif related to the sequence HphiHphiHphiphi (phi, a hydrophobic amino acid), are a superfamily of nucleotide hydrolases and transferases, which act on the alpha-phosphate of ribonucleotides, and contain a approximately 30 kDa domain that is typically either a homodimer of approximately 15 kDa polypeptides with two active-sites or an internally, imperfectly repeated polypeptide that retains a single HIT active site. On the basis of sequence, substrate specificity, structure, evolution, and mechanism, HIT proteins can be classified into the Hint branch, which consists of adenosine 5'-monophosphoramide hydrolases, the Fhit branch, which consists of diadenosine polyphosphate hydrolases, and the GalT branch, which consists of specific nucleoside monophosphate transferases, including galactose-1-phosphate uridylyltransferase, diadenosine tetraphosphate phosphorylase, and adenylyl sulfate:phosphate adenylytransferase. At least one human representative of each branch is lost in human diseases. Aprataxin, a Hint branch hydrolase, is mutated in ataxia-oculomotor apraxia syndrome. Fhit is lost early in the development of many epithelially derived tumors. GalT is deficient in galactosemia. Additionally, ASW is an avian Hint family member that has evolved to have unusual gene expression properties and the complete loss of its nucleotide binding site. The potential roles of ASW and Hint in avian sexual development are discussed elsewhere. Here we review what is known about biological activities of HIT proteins, the structural and biochemical bases for their functions, and propose a new enzyme mechanism for Hint and Fhit that may account for the differences between HIT hydrolases and transferases.

Acid Anhydride Hydrolases↗
PubMed1996

The structure of nucleotidylated histidine-166 of galactose-1-phosphate uridylyltransferase provides insight into phosphoryl group transfer.

Galactose-1-phosphate uridylyltransferase catalyzes the reaction of UDP-glucose with galactose 1-phosphate to form UDP-galactose and glucose 1-phosphate during normal cellular metabolism. The reaction proceeds through a double displacement mechanism characterized by the formation of a stable nucleotidylated histidine intermediate. This paper describes the preparation of the uridylyl-enzyme complex on the crystalline enzyme from Escherichia coli and its subsequent structure determination by X-ray crystallography. The refined structure has an R-factor of 19.6% (data between 65 and 1.86 A resolution) and reveals modest conformational changes at the active site compared to the inactive UMP/UDP-enzyme complex reported previously [Wedekind, J.E., Frey, P.A., & Rayment, I. (1995) Biochemistry 34, 11049-11061]. In particular, positions of the respective UMP alpha-phosphoryl groups differ by approximately 4 A. Well-defined electron density for the nucleotidylated imidazole supports the existence of a covalent bond between N epsilon 2 of the nucleophile and the alpha-phosphorus of UMP. A hydrogen bond that is conserved in both complexes between His 166 N delta 1 and the carbonyl O of His 164 serves to properly orient the nucleophile and electrostatically stabilize the positively charged imidazolium that results from nucleotidylation. Hydrogen bonds from side-chain Gln 168 to the nonbridging phosphoryl oxygens of the nucleotidyl intermediate appear crucial for the formation and reaction of the uridylyl-enzyme complex as well. The significance of the latter interaction is underscored by the fact that the predominant cause of the metabolic disease galactosemia is the mutation of the corresponding Gln (Gln 188 in humans) to Arg. A comparison to other phosphohistidyl enzymes is described, as well as a revised model for the mechanism of the uridylyltransferase.

Amino Acid Sequence↗
PubMed2004

Biosensor based on Langmuir-Blodgett films of poly(3-hexyl thiophene) for detection of galactose in human blood.

An amperometric biosensor was developed to estimate galactose in human blood serum. Monolayers of poly(3-hexyl thiophene) were placed on glass plates coated with indium tin oxide formed by dispensing a mixed solution of stearic acid in chloroform on to a water sub-phase. Galactose oxidase was mixed with poly(3-hexyl thiophene)/stearic acid in chloroform and dispensed on to the air-water interface of Langmuir-Blodgett trough. These monolayers were transferred on to glass plates which were used as working electrodes with platinum as a reference electrode. The amperometric galactose biosensor thus fabricated had a linear response from 0.05 to 0.5 g galactose l(-1) in blood serum. The normal level in blood is < 0.05 g galactose l(-1) in adults and 0-0.2 g galactose l(-1) in infants. In case of galactosemia, this increases to above 0.2 g galactose l(-1) in infants.

Adult↗
PubMed1995

Time-dependent aspects of osmolyte changes in rat kidney, urine, blood and lens with sorbinil and galactose feeding.

Sorbitol plus myo-inositol, betaine and glycerophosphorylcholine (GPC) are cellular osmolytes in the mammalian renal medulla. Galactosemia and hyperglycemia can cause excessive levels of galactitol or sorbitol in several organs via aldose reductase (AR) catalysis. AR inhibitors can reduce these polyols. To examine osmolyte responses to polyol perturbations, male Wistar rats were fed normal diet, the AR inhibitor sorbinil (at 40 mg/kg/d), 25% galactose, or a combination, for 10, 21 and 42 days. All animals at 21 days had higher apparent renal AR activity than at 10 or 42 days, possibly providing resistance to sorbinil. Sorbinil feeding alone tended to increase urinary, plasma and renal urea levels. It reduced AR activity and sorbitol contents in renal inner medulla, though less so at 21 days; other renal osmolytes, especially betaine, were elevated. Galactose feeding caused little change in renal AR activity, and resulted in high galactose and galactitol contents in renal medulla, urine, blood and lens (and higher renal Na+ contents at 10 days). Renal sorbitol, inositol and GPC decreased, while betaine contents trended higher at all times. Sorbinilgalactose feeding reduced renal AR activities and galactitol contents (again less so at 21 days), urine, blood and lens galactitol, and further reduced renal sorbitol contents. At 10 and 21 days it tended to raise renal betaine more, and restore inositol (but not GPC) contents to control levels. At 42 days it reduced renal and urinary Na+ and galactose, and decreased renal betaine to control levels. Under most conditions, total renal (non-urea) organic osmolyte contents (presumed to be mostly intracellular) and Na+ plus galactose contents (presumed mostly extracellular) changed together such that cell volumes may have been maintained. The exception was 10 days on galactose, where total osmolytes appeared too low. In galactose-fed animals, urine/plasma ratios suggest some renal galactitol efflux, and cellular galactitol probably helps maintain osmotic balance rather than cause swelling.

Aldehyde Reductase↗
PubMed1997

Crystal structures of HINT demonstrate that histidine triad proteins are GalT-related nucleotide-binding proteins.

Histidine triad nucleotide-binding protein (HINT), a dimeric purine nucleotide-binding protein from rabbit heart, is a member of the HIT (histidine triad) superfamily which includes HINT homologues and FHIT (HIT protein encoded at the chromosome 3 fragile site) homologues. Crystal structures of HINT-nucleotide complexes demonstrate that the most conserved residues in the superfamily mediate nucleotide binding and that the HIT motif forms part of the phosphate binding loop. Galactose-1-phosphate uridylyltransferase, whose deficiency causes galactosemia, contains tandem HINT domains with the same fold and mode of nucleotide binding as HINT despite having no overall sequence similarity. Features of FHIT, a diadenosine polyphosphate hydrolase and candidate tumour suppressor, are predicted from HINT-nucleotide structures.

Amino Acid Sequence↗
PubMed2002

Cerebellar granular layer aplasia in congenital hydrocephalus.

An unusual case of cerebellar granular layer aplasia is reported. A 5-year-old boy was born with hydrocephalus and a peritoneal drainage shunt was placed after the delivery. Symptoms of cerebral paralysis, impaired mental function and cerebellar ataxia had developed gradually. Patient's karyotype was 46,XY. Laboratory tests for cytomegalovirus, Herpes simplex virus, Toxoplasma gondii, human immunodeficiency virus, rubella and hepatitis B virus were negative. Further laboratory investigation showed no signs of Tay-Sachs disease, Niemann-Pick disease, Gaucher disease, phenylketonuria, galactosemia or glycogen storage disease. No congenital malformations were traced in other family members for three generations. Radiation exposure and infections during the pregnancy were refuted.

Cerebellum↗
PubMed1999

Non-enzymatic glycation of lens proteins and haemoglobin-inhibition by pyruvate: an in-vivo study.

AIM: Previous studies have demonstrated that pyruvate can prevent protein glycation and oxidative stress under in-vitro conditions. The aim of this study was to examine the in-vivo effectiveness of this metabolite against glycation of lens crystallins and haemoglobin in galactosemic rats. METHODS: Sprague-Dawley rats were maintained on a 30% or 50% galactose-containing diet in the absence or presence of 2% or 5% pyruvate in food and water, respectively. The animals were killed subsequently and the extent of glycation of lens crystallins and haemoglobin was determined using an affinity column chromatograpic technique. RESULTS: Maintenance of rats on the high galactose diet resulted in a significant increase in glycation of both the proteins. The increase was faster and more substantial in the animals maintained on the 50% galactose diet than that in the animals fed a 30% galactose diet. The increase in the latter was also very significant. Supplementation with pyruvate inhibited the process. CONCLUSION: The inhibition is attributable to a competitive binding of pyruvate to the protein NH2 groups as well as to the antioxidant effect of the compound. The studies therefore suggest that this and other alpha-keto-acids may be physiologically useful in minimizing glycation and oxidative stress induced tissue pathology by the hyperglycaemic conditions, such as diabetes and galactosemia. The results are also considered pharmacologically significant.

Animals↗
PubMed1999

[Familial cataract in plasma galactitol increase without known enzyme defect].

BACKGROUND: Several enzyme defects of the galactose pathway may lead to cataract formation. We report on a family with familiar cataract. PATIENTS: A 2-year-old Turkish girl (daughter of first cousins) presented with dense cortical and subcapsular opacifications and mature cataract respectively. Bilateral phacectomy, planned posterior capsulotomy, transpapillary vitrectomy and implantation of a posterior chamber lens were performed. The child was otherwise healthy and the pregnancy had been unremarkable. The 25-year-old mother showed circumscribed drop-like opacities of the lens cortex bilaterally, the 5-year-old sister a diffuse opacification of the lens cortex in both eyes, the 27-year-old father and the 13-year-old uncle clear lenses. RESULTS: The girl's level of galactitol was elevated to 2.8 nmol/ml in the plasma (normal values 0.25-1.13 nmol/ml) and to 3.1 nmol/mg protein in the lens (normal values 0.5-1.7 nmol/mg protein). The levels of galactose-1-phosphate in RBC and sorbitol in plasma were in the normal range. The enzyme activities of galactokinase, galactose-1-phosphate uridyl transferase, UDP-galactose epimerase and sorbitol dehydrogenase in RBC, as well as the sorbitol dehydrogenase activity in the lens were in the normal range. The sister and the uncle both had slightly elevated plasma galactitol levels. CONCLUSIONS: Cataract-formation in this family is most likely due to a defect in the galactitol pathway, e.g. cataract in galactosemia without known enzyme defect (Shin-Jakobs disease). In patients with unexplained congenital or infantile cataracts, disorders of the polyol pathway should be thoroughly checked for to ensure a therapeutic diet if necessary.

Adult↗
PubMed1980

[12 years Austrian newborn screening for inborn errors of metabolism. Results with special reference to phenylketonuria, hyperphenylalaninemia and histidinemia (author's transl)].

The Austrian Screening Program performed during the last 12 years 5,833.381 tests in 1,003.841 newborns to detect at last 10 different disorders. 225 cases were uncovered: 81 PKU, 1 Dihydropteridine-Reductase-Deficiency, 37 Hyperphenylalaninemias of long duration, 23 Galactosemias by Transferase deficiency, 6 by Kinase deficiency, 1 Leucinosis, 1 Homocystinuria, 54 Histidinemias, 2 Arginino-Succinic-Acidurias, 3 alpha-1-Antitrypsin-Inhibitor-Deficiencies, 15 Hypothyroidism as well as 1 Phosphoglucomutase-Deficiency. Since 1976 97% of all live births were tested. Except in Hypothyroidism in Austria also treatment and follow-up are centralized. This makes a higher treatment quality and important observations possible. In PKU-patients there is a decline in EQ/IQ between 1 and 6 to 8 years of age of 13 points in average (105--92). This decline can not be correlated with treatment introduction age (26.4 days) and treatment quality. Since also the parents IQ's are significantly below the IQ's of a recent control group and mothers IQ are paralleling the IQ's of their PKU children the decline seems to be a phenylalanine-blood-level-independent phenomenon. Also one quarter of the patients with Histidinemia shows the same IQ decline. The difference between Bühler-Hetzer and Kramer results at 4 years of age seem to have prognostic value. Comparison for 1978 of the expenses of the total screening plus the one of diet in 59 PKU patients already psychometrically tested (average IQ 100) with the expense for institutionalisation of the same 59 shows the former 5 million A.S. lower.

Austria↗
PubMed1993

[Treatable diseases of the nervous system with cataract formation].

The detection of a cataract in combination with a neurological deficit may provide the physician with important diagnostic help. But a minority of underlying diseases (angiokeratoma corporis diffusum, cerebrotendinous xanthomatosis, diabetes mellitus, galactosemia, hypocalcemia, Refsum's disease, Wilson's disease; Charles Bonnet syndrome; relapsing Perichondritis; adverse effects of medication and intoxications) can be treated causally. Therefore they are summed up and discussed in this paper.

Cataract↗
PubMed1979

Cytoplasmic phase separation in formation of galactosemic cataract in lenses of young rats.

We have determined the age dependence of the characteristics of the cytoplasmic phase separation of lenses from normal and galactosemic young rats. In the normal lens, the temperature at which the phase separation occurs decreases monotonically with age. In the lenses of rats fed with a high galactose diet, the phase separation temperature becomes increasingly higher with the development of galactosemia. When the phase separation temperature becomes higher than the ocular temperature, the nuclear opacity appears in vivo. The opacity is the result of light scattering by spatial fluctuations of the refractive index formed by interspersed regions of two separated phases in the fiber cell cytoplasm. This shows that the nuclear opacity that develops in the lens of galactosemic rats is the manifestation of phase separation of the lens fiber cytoplasm.

Journal Article↗
PubMed1992

Cloning of a human galactokinase gene (GK2) on chromosome 15 by complementation in yeast.

A human cDNA encoding a galactokinase (EC 2.7.1.6) was isolated by complementation of a galactokinase-deficient (gal1-) strain of Saccharomyces cerevisiae. This cDNA encodes a predicted protein of 458 amino acids with 29% identity to galactokinase of Saccharomyces carlsbergensis. Previous studies have mapped a human galactokinase gene (GK1) to chromosome 17q23-25, closely linked to thymidine kinase. The galactokinase gene that we have isolated (GK2) is located on chromosome 15. The relationship between the disease locus for galactokinase deficiency galactosemia, which is responsible for cataracts in newborns and possibly presenile cataracts in adults, and the two galactokinase loci is unknown.

Amino Acid Sequence↗
PubMed1999

The biochemical role of glutamine 188 in human galactose-1-phosphate uridyltransferase.

The substitution of arginine for glutamine at amino acid 188 (Q188R) ablates the function of human galactose-1-phosphate uridyltransferase (GALT) and is the most common mutation causing galactosemia in the white population. GALT catalyzes two consecutive reactions. The first reaction binds UDP-glucose (UDP-Glu), displaces glucose-1-phosphate (glu-1-P), and forms the UMP-GALT intermediate. In the second reaction, galactose-1-phosphate (gal-1-P) is bound, UDP-galactose (UDP-Gal) is released, and the free enzyme is recycled. In this study, we modeled glutamine, asparagine, and a common mutation arginine at amino acid 188 on the three-dimensional model of the Escherichia coli GALT-UMP protein crystal. We found that the amide group of the glutamine side chain could provide two hydrogen bonds to the phosphoryl oxygens of UMP with lengths of 2.52 and 2.82 A. Arginine and asparagine could provide only one hydrogen bond of 2. 52 and 3.02 A, respectively. To test this model, we purified recombinant human Gln188-, Arg188-, and Asn188-GALT and analyzed the first reaction in the absence of gal-1-P by quantitating glu-1-P released using enzyme-linked methods. Gln188-GALT displaced 80 +/- 7. 0 nmol glu-1-P/mg GALT/min in the first reaction. By contrast, both Arg188- and Asn188-GALT released more glu-1-P (170 +/- 8.0 and 129 +/- 28.4 nmol/mg GALT/min, respectively). The overall, double displacement reaction was quantitated in the presence of gal-1-P. Gln188-GALT produced 80,030 +/- 5,910 nmol glu-1-P/mg GALT/min, whereas the mutant Arg188- and Asn188-GALT released only 600 +/- 71. 2 and 2960 +/- 283.6 nmole glu-1-P/mg GALT/min, respectively. We conclude from these data that glutamine at position 188 stabilizes the UMP-GALT intermediate through hydrogen bonding and enables the double displacement of both glu-1-P and UDP-Gal. The substitution of arginine or asparagine at position 188 reduces hydrogen bonding and destabilizes UMP-GALT. The unstable UMP-GALT allows single displacement of glu-1-P with release of free GALT but impairs the subsequent binding of gal-1-P and displacement of UDP-Gal.

Amino Acid Sequence↗
PubMed2000

Functional consequence of substitutions at residue 171 in human galactose-1-phosphate uridylyltransferase.

Impairment of the human enzyme galactose-1-phosphate uridylyltransferase (hGALT) results in the potentially lethal disorder classic galactosemia. Although a variety of naturally occurring mutations have been identified in patient alleles, few have been well characterized. We have explored the functional significance of a common patient mutation, F171S, using a strategy of conservative substitution at the defined residue followed by expression of the wild-type and, alternatively, substituted proteins in a null-background strain of yeast. As expected from patient studies, the F171S-hGALT protein demonstrated <0.1% wild-type levels of activity, although two of three conservatively substituted moieties, F171L- and F171Y-hGALT, demonstrated approximately 10% and approximately 4% activity, respectively. The third protein, F171W, demonstrated severely reduced abundance, precluding further study. Detailed kinetic analyses of purified wild-type, F171L- and F171Y-hGALT enzymes, coupled with homology modeling of these proteins, enabled us to suggest that the effects of these substitutions resulted largely from altering the position of a catalytically important residue, Gln-188, and secondarily, by altering the subunit interface and perturbing hexose binding to the uridylylated enzyme. These results not only provide insight into the functional impact of a single common patient allele and offer a paradigm for similar studies of other clinically or biochemically important residues, but they further help to elucidate activity of the wild-type human GALT enzyme.

Amino Acid Substitution↗
PubMed2000

Covalent heterogeneity of the human enzyme galactose-1-phosphate uridylyltransferase.

Galactose-1-phosphate uridylyltransferase (GALT) acts by a double displacement mechanism, catalyzing the second step in the Leloir pathway of galactose metabolism. Impairment of this enzyme results in the potentially lethal disorder, galactosemia. Although the microheterogeneity of native human GALT has long been recognized, the biochemical basis for this heterogeneity has remained obscure. We have explored the possibility of covalent GALT heterogeneity using denaturing two-dimensional gel electrophoresis and Western blot analysis to fractionate and visualize hemolysate hGALT, as well as the human enzyme expressed in yeast. In both contexts, two predominant GALT species were observed. To define the contribution of uridylylated enzyme intermediate to the two-spot pattern, we exploited the null allele, H186G-hGALT. The Escherichia coli counterpart of this mutant protein (H166G-eGALT) has previously been demonstrated to fold properly, although it cannot form covalent intermediate. Analysis of the H186G-hGALT protein demonstrated a single predominant species, implicating covalent intermediate as the basis for the second spot in the wild-type pattern. In contrast, three naturally occurring mutations, N314D, Q188R, and S135L-hGALT, all demonstrated the two-spot pattern. Together, these data suggest that uridylylated hGALT comprises a significant fraction of the total GALT enzyme pool in normal human cells and that three of the most common patient mutations do not disrupt this distribution.

Catalytic Domain↗
PubMed2003

Iron requirement for GAL gene induction in the yeast Saccharomyces cerevisiae.

Iron is an essential nutrient. Its deficiency hinders the synthesis of ATP and DNA. We report that galactose metabolism is defective when iron availability is restricted. Our data support this connection because 1) galactose-mediated induction of GAL promoter-dependent gene expression was diminished by iron limitation, and 2) iron-deficient mutants grew slowly on galactose-containing medium. These two defects were immediately corrected by iron replacement. Inherited defects in human galactose metabolism are characteristic of the disease called galactosemia. Our findings suggest that iron-deficient galactosemic individuals might be more severely compromised than iron-replete individuals. This work shows that iron homeostasis and galactose metabolism are linked with one another.

Cell Division↗
PubMed2006

Relationship between UDP-galactose 4'-epimerase activity and galactose sensitivity in yeast.

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.

Cell Extracts↗