UDP-glucose 4-epimerase
| UDP-glucose 4-epimerase | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Aliases | UDPgalactose 4-epimerase4-epimeraseuridine diphosphate glucose 4-epimeraseUDPG-4-epimeraseUDP-galactose 4-epimeraseuridine diphosphoglucose epimeraseuridine diphospho-galactose-4-epimeraseUDP-D-galactose 4-epimeraseUDP-glucose epimeraseuridine diphosphoglucose 4-epimeraseuridine diphosphate galactose 4-epimerase | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | GeneCards:[1];OMA:- orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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| Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| UDP-glucose 4-epimerase | |||||||||
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 H. sapiensUDP-glucose 4-epimerase homodimer bound toNADHandUDP-glucose.Domains:N-terminalandC-terminal. | |||||||||
| Identifiers | |||||||||
| EC no. | 5.1.3.2 | ||||||||
| CAS no. | 9032-89-7 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDBstructures | RCSB PDBPDBePDBsum | ||||||||
| Gene Ontology | AmiGO/QuickGO | ||||||||
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| UDP-galactose-4-epimerase | |||||||
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 Human GALE bound toNAD+andUDP-GlcNAc,withN-andC-terminaldomains highlighted.Asn 207contorts to accommodate UDP-GlcNAc within the active site. | |||||||
| Identifiers | |||||||
| Symbol | GALE | ||||||
| NCBI gene | 2582 | ||||||
| HGNC | 4116 | ||||||
| OMIM | 606953 | ||||||
| RefSeq | NM_000403 | ||||||
| UniProt | Q14376 | ||||||
| Other data | |||||||
| EC number | 5.1.3.2 | ||||||
| Locus | Chr. 1p36-p35 | ||||||
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| NAD-dependent epimerase/dehydratase | |||||||||
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| Identifiers | |||||||||
| Symbol | ? | ||||||||
| Pfam | PF01370 | ||||||||
| InterPro | IPR001509 | ||||||||
| Membranome | 330 | ||||||||
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TheenzymeUDP-glucose 4-epimerase(EC5.1.3.2), also known asUDP-galactose 4-epimeraseorGALE,is a homodimeric epimerase found in bacterial, fungal, plant, and mammalian cells. This enzyme performs the final step in theLeloir pathwayofgalactosemetabolism, catalyzing the reversible conversion ofUDP-galactosetoUDP-glucose.[1]GALE tightly bindsnicotinamide adenine dinucleotide(NAD+), a co-factor required for catalytic activity.[2]
Additionally, human and some bacterial GALE isoforms reversibly catalyze the formation of UDP-N-acetylgalactosamine (UDP-GalNAc) from UDP-N-acetylglucosamine (UDP-GlcNAc) in the presence of NAD+, an initial step inglycoproteinorglycolipidsynthesis.[3]
Historical significance
[edit]Dr.Luis Leloirdeduced the role of GALE in galactose metabolism during his tenure at the Instituto de Investigaciones Bioquímicas del Fundación Campomar, initially terming the enzyme waldenase.[4]Dr. Leloir was awarded the 1970Nobel Prize in Chemistryfor his discovery of sugar nucleotides and their role in the biosynthesis of carbohydrates.[5]
Structure
[edit]GALE belongs to the short-chain dehydrogenase/reductase (SDR) superfamily of proteins.[6]This family is characterized by a conserved Tyr-X-X-X-Lys motif necessary for enzymatic activity; one or moreRossmann foldscaffolds; and the ability to bind NAD+.[6]
Tertiary structure
[edit]GALE structure has been resolved for a number of species, includingE. coli[7]and humans.[8]GALE exists as a homodimer in various species.[8]
While subunit size varies from 68 amino acids(Enterococcus faecalis)to 564 amino acids(Rhodococcus jostii),a majority of GALE subunits cluster near 330 amino acids in length.[6]Each subunit contains two distinct domains. An N-terminal domain contains a 7-stranded parallel β-pleated sheet flanked by α-helices.[1]PairedRossmann foldswithin this domain allow GALE to tightly bind one NAD+cofactor per subunit.[2]A 6-stranded β-sheet and 5 α-helices comprise GALE's C-terminal domain.[1]C-terminal residues bind UDP, such that the subunit is responsible for correctly positioning UDP-glucose or UDP-galactose for catalysis.[1]
Active site
[edit]The cleft between GALE's N- and C-terminal domains constitutes the enzyme'sactive site.A conserved Tyr-X-X-X Lys motif is necessary for GALE catalytic activity; in humans, this motif is represented by Tyr 157-Gly-Lys-Ser-Lys 161,[6]whileE. coliGALE contains Tyr 149-Gly-Lys-Ser-Lys 153.[8]The size and shape of GALE's active site varies across species, allowing for variable GALE substrate specificity.[3]Additionally, the conformation of the active site within a species-specific GALE is malleable; for instance, a bulky UDP-GlcNAc 2' N-acetyl group is accommodated within the human GALE active site by the rotation of the Asn 207 carboxamide side chain.[3]
| Residue | Function |
|---|---|
| Ala 216, Phe 218 | Anchor uracil ring to enzyme. |
| Asp 295 | Interacts with ribose 2' hydroxyl group. |
| Asn 179, Arg 231, Arg 292 | Interact with UDP phosphate groups. |
| Tyr 299, Asn 179 | Interact with galactose 2' hydroxyl or glucose 6' hydroxyl group; properly position sugar within active site. |
| Tyr 177, Phe 178 | Interact with galactose 3' hydroxyl or glucose 6' hydroxyl group; properly position sugar within active site. |
| Lys 153 | Lowers pKa of Tyr 149, allows for abstraction or donation of a hydrogen atom to or from the sugar 4' hydroxyl group. |
| Tyr 149 | Abstracts or donates a hydrogen atom to or from the sugar 4' hydroxyl group, catalyzing formation of 4-ketopyranose intermediate. |
Mechanism
[edit]Conversion of UDP-galactose to UDP-glucose
[edit]GALE inverts the configuration of the 4' hydroxyl group of UDP-galactose through a series of 4 steps. Upon binding UDP-galactose, a conserved tyrosine residue in the active site abstracts a proton from the 4' hydroxyl group.[7][10]
Concomitantly, the 4' hydride is added to thesi-face of NAD+, generating NADH and a 4-ketopyranose intermediate.[1]The 4-ketopyranose intermediate rotates 180° about the pyrophosphoryl linkage between the glycosyl oxygen and β-phosphorus atom, presenting the opposite face of the ketopyranose intermediate to NADH.[10]Hydride transfer from NADH to this opposite face inverts the stereochemistry of the 4' center. The conserved tyrosine residue then donates its proton, regenerating the 4' hydroxyl group.[1]
Conversion of UDP-GlcNAc to UDP-GalNAc
[edit]Human and some bacterial GALE isoforms reversibly catalyze the conversion of UDP-GlcNAc to UDP-GalNAc through an identical mechanism, inverting the stereochemical configuration at the sugar's 4' hydroxyl group.[3][11]
Biological function
[edit]
Galactose metabolism
[edit]No direct catabolic pathways exist for galactose metabolism. Galactose is therefore preferentially converted intoglucose-1-phosphate,which may be shunted intoglycolysisor theinositolsynthesis pathway.[12]
GALE functions as one of four enzymes in theLeloir pathwayof galactose conversion of glucose-1-phosphate. First,galactose mutarotaseconverts β-D-galactose to α-D-galactose.[1]Galactokinase then phosphorylates α-D-galactose at the 1' hydroxyl group, yieldinggalactose-1-phosphate.[1]In the third step,galactose-1-phosphate uridyltransferasecatalyzes the reversible transfer of a UMP moiety from UDP-glucose to galactose-1-phosphate, generating UDP-galactose and glucose-1-phosphate.[1]In the final Leloir step, UDP-glucose is regenerated from UDP-galactose by GALE; UDP-glucose cycles back to the third step of the pathway.[1]As such, GALE regenerates a substrate necessary for continued Leloir pathway cycling.
The glucose-1-phosphate generated in step 3 of the Leloir pathway may be isomerized toglucose-6-phosphatebyphosphoglucomutase.Glucose-6-phosphate readily enters glycolysis, leading to the production of ATP and pyruvate.[13]Furthermore, glucose-6-phosphate may be converted toinositol-1-phosphatebyinositol-3-phosphate synthase,generating a precursor needed forinositolbiosynthesis.[14]
UDP-GalNAc synthesis
[edit]Human and selected bacterial GALE isoforms bind UDP-GlcNAc, reversibly catalyzing its conversion to UDP-GalNAc. A family ofglycosyltransferasesknown as UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosamine transferases (ppGaNTases) transfers GalNAc from UDP-GalNAc to glycoprotein serine and threonine residues.[15]ppGaNTase-mediated glycosylation regulates protein sorting,[16][17][18][19][20]ligand signaling,[21][22][23]resistance to proteolytic attack,[24][25]and represents the first committed step in mucin biosynthesis.[15]
Role in disease
[edit]Human GALE deficiency or dysfunction results in Type IIIgalactosemia,which may exist in a mild (peripheral) or more severe (generalized) form.[12]
References
[edit]- ^abcdefghijkHolden HM, Rayment I, Thoden JB (November 2003)."Structure and function of enzymes of the Leloir pathway for galactose metabolism".J. Biol. Chem.278(45): 43885–8.doi:10.1074/jbc.R300025200.PMID12923184.
- ^abLiu Y, Vanhooke JL, Frey PA (June 1996). "UDP-galactose 4-epimerase: NAD+ content and a charge-transfer band associated with the substrate-induced conformational transition".Biochemistry.35(23): 7615–20.doi:10.1021/bi960102v.PMID8652544.
- ^abcdThoden JB, Wohlers TM, Fridovich-Keil JL, Holden HM (May 2001)."Human UDP-galactose 4-epimerase. Accommodation of UDP-N-acetylglucosamine within the active site".J. Biol. Chem.276(18): 15131–6.doi:10.1074/jbc.M100220200.PMID11279032.
- ^LELOIR LF (September 1951). "The enzymatic transformation of uridine diphosphate glucose into a galactose derivative".Arch Biochem.33(2): 186–90.doi:10.1016/0003-9861(51)90096-3.hdl:11336/140700.PMID14885999.
- ^"The Nobel Prize in Chemistry 1970"(Press release). The Royal Swedish Academy of Science. 1970.Retrieved2010-05-17.
- ^abcdKavanagh KL, Jörnvall H, Persson B, Oppermann U (December 2008)."Medium- and short-chain dehydrogenase/reductase gene and protein families: the SDR superfamily: functional and structural diversity within a family of metabolic and regulatory enzymes".Cell. Mol. Life Sci.65(24): 3895–906.doi:10.1007/s00018-008-8588-y.PMC2792337.PMID19011750.
- ^abPDB:1EK5;Thoden JB, Wohlers TM, Fridovich-Keil JL, Holden HM (May 2000). "Crystallographic evidence for Tyr 157 functioning as the active site base in human UDP-galactose 4-epimerase".Biochemistry.39(19): 5691–701.doi:10.1021/bi000215l.PMID10801319.
- ^abcPDB:1XEL;Thoden JB, Frey PA, Holden HM (April 1996). "Molecular structure of the NADH/UDP-glucose abortive complex of UDP-galactose 4-epimerase from Escherichia coli: implications for the catalytic mechanism".Biochemistry.35(16): 5137–44.doi:10.1021/bi9601114.PMID8611497.
- ^PDB:1A9Z;Thoden JB, Holden HM (August 1998). "Dramatic differences in the binding of UDP-galactose and UDP-glucose to UDP-galactose 4-epimerase from Escherichia coli".Biochemistry.37(33): 11469–77.doi:10.1021/bi9808969.PMID9708982.
- ^abLiu Y, Thoden JB, Kim J, Berger E, Gulick AM, Ruzicka FJ, Holden HM, Frey PA (September 1997). "Mechanistic roles of tyrosine 149 and serine 124 in UDP-galactose 4-epimerase from Escherichia coli".Biochemistry.36(35): 10675–84.doi:10.1021/bi970430a.PMID9271498.
- ^Kingsley DM, Kozarsky KF, Hobbie L, Krieger M (March 1986). "Reversible defects in O-linked glycosylation and LDL receptor expression in a UDP-Gal/UDP-GalNAc 4-epimerase deficient mutant".Cell.44(5): 749–59.doi:10.1016/0092-8674(86)90841-X.PMID3948246.S2CID28293937.
- ^abLai K, Elsas LJ, Wierenga KJ (November 2009)."Galactose toxicity in animals".IUBMB Life.61(11): 1063–74.doi:10.1002/iub.262.PMC2788023.PMID19859980.
- ^Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (2008).Biochemistry (Looseleaf).San Francisco: W. H. Freeman. pp.443–58.ISBN9780716718437.
- ^Michell RH (February 2008). "Inositol derivatives: evolution and functions".Nat. Rev. Mol. Cell Biol.9(2): 151–61.doi:10.1038/nrm2334.PMID18216771.S2CID3245927.
- ^abTen Hagen KG, Fritz TA, Tabak LA (January 2003)."All in the family: the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases".Glycobiology.13(1): 1R–16R.doi:10.1093/glycob/cwg007.PMID12634319.
- ^Alfalah M, Jacob R, Preuss U, Zimmer KP, Naim H, Naim HY (June 1999)."O-linked glycans mediate apical sorting of human intestinal sucrase-isomaltase through association with lipid rafts".Curr. Biol.9(11): 593–6.doi:10.1016/S0960-9822(99)80263-2.PMID10359703.S2CID16866875.
- ^Altschuler Y, Kinlough CL, Poland PA, Bruns JB, Apodaca G, Weisz OA, Hughey RP (March 2000)."Clathrin-mediated endocytosis of MUC1 is modulated by its glycosylation state".Mol. Biol. Cell.11(3): 819–31.doi:10.1091/mbc.11.3.819.PMC14813.PMID10712502.
- ^Breuza L, Garcia M, Delgrossi MH, Le Bivic A (February 2002). "Role of the membrane-proximal O-glycosylation site in sorting of the human receptor for neurotrophins to the apical membrane of MDCK cells".Exp. Cell Res.273(2): 178–86.doi:10.1006/excr.2001.5442.PMID11822873.
- ^Naim HY, Joberty G, Alfalah M, Jacob R (June 1999)."Temporal association of the N- and O-linked glycosylation events and their implication in the polarized sorting of intestinal brush border sucrase-isomaltase, aminopeptidase N, and dipeptidyl peptidase IV".J. Biol. Chem.274(25): 17961–7.doi:10.1074/jbc.274.25.17961.PMID10364244.
- ^Zheng X,Sadler JE(March 2002)."Mucin-like domain of enteropeptidase directs apical targeting in Madin-Darby canine kidney cells".J. Biol. Chem.277(9): 6858–63.doi:10.1074/jbc.M109857200.PMID11878264.
- ^Hooper LV, Gordon JI (February 2001)."Glycans as legislators of host-microbial interactions: spanning the spectrum from symbiosis to pathogenicity".Glycobiology.11(2): 1R–10R.doi:10.1093/glycob/11.2.1R.PMID11287395.
- ^Yeh JC, Hiraoka N, Petryniak B, Nakayama J, Ellies LG, Rabuka D, Hindsgaul O, Marth JD, Lowe JB, Fukuda M (June 2001)."Novel sulfated lymphocyte homing receptors and their control by a Core1 extension beta 1,3-N-acetylglucosaminyltransferase".Cell.105(7): 957–69.doi:10.1016/S0092-8674(01)00394-4.PMID11439191.S2CID18674112.
- ^Somers WS, Tang J, Shaw GD, Camphausen RT (October 2000)."Insights into the molecular basis of leukocyte tethering and rolling revealed by structures of P- and E-selectin bound to SLe(X) and PSGL-1".Cell.103(3): 467–79.doi:10.1016/S0092-8674(00)00138-0.PMID11081633.S2CID12719907.
- ^Sauer J, Sigurskjold BW, Christensen U, Frandsen TP, Mirgorodskaya E, Harrison M, Roepstorff P, Svensson B (December 2000). "Glucoamylase: structure/function relationships, and protein engineering".Biochim. Biophys. Acta.1543(2): 275–293.doi:10.1016/s0167-4838(00)00232-6.PMID11150611.
- ^Garner B, Merry AH, Royle L, Harvey DJ, Rudd PM, Thillet J (June 2001)."Structural elucidation of the N- and O-glycans of human apolipoprotein(a): role of o-glycans in conferring protease resistance".J. Biol. Chem.276(25): 22200–8.doi:10.1074/jbc.M102150200.PMID11294842.
Further reading
[edit]- Leloir LF (1953). "Enzymic Isomerization and Related Processes".Advances in Enzymology and Related Areas of Molecular Biology.Advances in Enzymology - and Related Areas of Molecular Biology. Vol. 14. pp. 193–218.doi:10.1002/9780470122594.ch6.ISBN9780470122594.PMID13057717.
{{cite book}}:|journal=ignored (help) - Maxwell ES, de Robichon-Szulmajster H (1960)."Purification of uridine diphosphate galactose-4-epimerase from yeast and the identification of protein-bound diphosphopyridine nucleotide".J. Biol. Chem.235(2): 308–312.doi:10.1016/S0021-9258(18)69520-1.
- Wilson DB, Hogness DS (August 1964)."The enzymes of the galactose operon in Escherichia coli. I Purification and characterization of uridine diphosphogalactose 4-epimerase".J. Biol. Chem.239:2469–81.doi:10.1016/S0021-9258(18)93876-7.PMID14235524.
External links
[edit]- GeneReviews/NCBI/NIH/UW entry on Epimerase Deficiency Galactosemia
- OMIM entries on Epimerase Deficiency Galactosemia
- UDPgalactose+4-Epimeraseat the U.S. National Library of MedicineMedical Subject Headings(MeSH)
- ^Beebe, Jane A.; Frey, Perry A. (1998-10-01)."Galactose Mutarotase: Purification, Characterization, and Investigations of Two Important Histidine Residues".Biochemistry.37(42): 14989–14997.doi:10.1021/bi9816047.ISSN0006-2960.