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22  structures 1465  species 3  interactions 1674  sequences 25  architectures

Family: GalP_UDP_transf (PF01087)

Summary: Galactose-1-phosphate uridyl transferase, N-terminal domain

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This is the Wikipedia entry entitled "Galactose-1-phosphate uridylyltransferase". More...

Galactose-1-phosphate uridylyltransferase Edit Wikipedia article

Galactose-1-phosphate uridylyltransferase 1GUP.png
Available structures
PDB Ortholog search: PDBe RCSB
Aliases GALT, entrez:2592
External IDs OMIM: 606999 MGI: 95638 HomoloGene: 126 GeneCards: 2592
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr 9: 34.64 – 34.65 Mb Chr 4: 41.76 – 41.76 Mb
PubMed search [1] [2]
View/Edit Human View/Edit Mouse
Galactose-1-phosphate uridyl transferase, N-terminal domain
Symbol GalP_UDP_transf
Pfam PF01087
Pfam clan CL0265
SCOP 1hxp
Galactose-1-phosphate uridyl transferase, C-terminal domain
PDB 1gup EBI.jpg
structure of nucleotidyltransferase complexed with udp-galactose
Symbol GalP_UDP_tr_C
Pfam PF02744
Pfam clan CL0265
InterPro IPR005850
SCOP 1hxp

Galactose-1-phosphate uridylyltransferase (or GALT) is an enzyme (EC responsible for converting ingested galactose to glucose.[3]

Galactose-1-phosphate uridylyltransferase (GALT) catalyzes the second step of the Leloir pathway of galactose metabolism, namely:

UDP-glucose + galactose 1-phosphate glucose 1-phosphate + UDP-galactose

The expression of GALT is controlled by the actions of the FOXO3 gene. The absence of this enzyme results in classic galactosemia in humans and can be fatal in the newborn period if lactose is not removed from the diet. The pathophysiology of galactosemia has not been clearly defined.[3]


GALT catalyzes the second reaction of the Leloir pathway of galactose metabolism through ping pong bi-bi kinetics with a double displacement mechanism.[4] This means that the net reaction consists of two reactants and two products (see reaction above), and it proceeds by the following mechanism: the enzyme reacts with one substrate to generate one product and a modified enzyme, which goes on to react with the second substrate to make the second product while regenerating the original enzyme.[5] In the case of GALT, the His166 residue acts as a potent nucleophile to facilitate transfer of a nucleotide between UDP-hexoses and hexose-1-phosphates.[6]

  1. UDP-glucose + E-His ⇌ Glucose-1-phosphate + E-His-UMP
  2. Galactose-1-phosphate + E-His-UMP ⇌ UDP-galactose + E-His[6]
Two-step action of galactose-1-phosphate uridylyltransferase. Image adapted from [7]

Structural studies

The three-dimensional structure at 180 pm resolution (x-ray crystallography) of GALT was discovered by Wedekind, Frey, and Rayment, and their structural analysis has found key amino acids essential for GALT function.[6]

The important amino acids that Wedekind et al. found in their structural analysis of GALT, such as Leu4, Phe75, Asn77, Asp78, Phe79, and Val108, are consistent with residues that have been implicated both in point mutation experiments as well as in clinical screening to play a role in human galactosemia.[6][8]

Clinical significance

Deficiency of GALT causes classic galactosemia. Galactosemia is a childhood disease of hereditary nature.[9] The autosomal recessive trait affects approximately 1 in every 40,000-60,000 live-born infants. Classical galactosemia (G/G) is caused by a deficiency in GALT activity, whereas the more common clinical affliction, Duarte/Classica (D/G) arises from attenuation of GALT activity.[10] Symptoms include ovarian failure, developmental coordination disorder (difficulty speaking correctly and consistently),[11] and neurologic deficits.[10] A single mutation in any of several amino acids can lead to attenuation or deficiency in GALT activity.[12] For example, a single mutation from A to G in exon 6 of the GALT gene changes Glu188 to an arginine, and a mutation from A to G in exon 10 converts Asn314 to an aspartic acid.[10] These two mutations also add new restriction enzyme cut sites, which enable detection by and large-scale population screening with PCR (polymerase chain reaction).[10] Screening has mostly eliminated neonatal death by G/G galactosemia, but the disease, due to GALT’s role in the biochemical metabolism of ingested galactose (which is toxic when accumulated) to the energetically useful glucose, can certainly be fatal.[9][13] However, those afflicted with galactosemia can live relatively normal lives by avoiding milk products and anything else containing galactose (since it cannot be metabolized), although there is the potential for problems in neurological development, or other complications, even in those who avoid galactose.[14]

Disease Database

Galactosemia (GALT) Mutation Database


  1. ^ "Human PubMed Reference:". 
  2. ^ "Mouse PubMed Reference:". 
  3. ^ a b "Entrez Gene: GALT galactose-1-phosphate uridylyltransferase". 
  4. ^ Wong LJ, Frey PA (September 1974). "Galactose-1-phosphate uridylyltransferase: rate studies confirming a uridylyl-enzyme intermediate on the catalytic pathway". Biochemistry. 13 (19): 3889–3894. doi:10.1021/bi00716a011. PMID 4606575. 
  5. ^
  6. ^ a b c d Wedekind JE, Frey PA, Rayment I (September 1995). "Three-dimensional structure of galactose-1-phosphate uridylyltransferase from Escherichia coli at 1.8 A resolution". Biochemistry. 34 (35): 11049–61. doi:10.1021/bi00035a010. PMID 7669762. 
  7. ^
  8. ^ Seyrantepe V, Ozguc M, Coskun T, Ozalp I, Reichardt JK (1999). "Identification of mutations in the galactose-1-phosphate uridyltransferase (GALT) gene in 16 Turkish patients with galactosemia, including a novel mutation of F294Y. Mutation in brief no. 235. Online". Hum. Mutat. 13 (4): 339. doi:10.1002/(SICI)1098-1004(1999)13:4<339::AID-HUMU18>3.0.CO;2-S. PMID 10220154. 
  9. ^ a b Fridovich-Keil JL (December 2006). "Galactosemia: the good, the bad, and the unknown". J. Cell. Physiol. 209 (3): 701–5. doi:10.1002/jcp.20820. PMID 17001680. 
  10. ^ a b c d Elsas LJ, Langley S, Paulk EM, Hjelm LN, Dembure PP (1995). "A molecular approach to galactosemia". Eur. J. Pediatr. 154 (7 Suppl 2): S21–7. doi:10.1007/BF02143798. PMID 7671959. 
  11. ^
  12. ^ Dobrowolski SF, Banas RA, Suzow JG, Berkley M, Naylor EW (February 2003). "Analysis of common mutations in the galactose-1-phosphate uridyl transferase gene: new assays to increase the sensitivity and specificity of newborn screening for galactosemia". J Mol Diagn. 5 (1): 42–7. doi:10.1016/S1525-1578(10)60450-3. PMC 1907369free to read. PMID 12552079. 
  13. ^ Lai K, Elsas LJ, Wierenga KJ (November 2009). "Galactose toxicity in animals". IUBMB Life. 61 (11): 1063–74. doi:10.1002/iub.262. PMC 2788023free to read. PMID 19859980. 
  14. ^

Further reading

External links

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Galactose-1-phosphate uridyl transferase, N-terminal domain Provide feedback

SCOP reports fold duplication with C-terminal domain. Both involved in Zn and Fe binding.

Literature references

  1. Wedekind JE, Frey PA, Rayment I; , Biochemistry 1995;34:11049-11061.: Three-dimensional structure of galactose-1-phosphate uridylyltransferase from Escherichia coli at 1.8 A resolution. PUBMED:7669762 EPMC:7669762

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR005849

Galactose-1-phosphate uridyl transferase catalyses the conversion of UDP-glucose and alpha-D-galactose 1-phosphate to alpha-D-glucose 1-phosphate and UDP-galactose during galactose metabolism. The enzyme is present in prokaryotes and eukaryotes. Defects in GalT in humans is the cause of galactosemia, an inherited disorder of galactose metabolism that leads to jaundice, cataracts and mental retardation.

This domain describes the C-terminal of Galactose-1-phosphate uridyl transferase. SCOP reports fold duplication of the C-terminal with the N-terminal domain. Both are involved in Zn and Fe binding

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

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Pfam Clan

This family is a member of clan HIT (CL0265), which has the following description:

The HIT superfamily are a superfamily of nucleotide hydrolases and transferases, which act on the alpha-phosphate of ribonucleotides [1].

The clan contains the following 8 members:

CDH CwfJ_C_1 DcpS_C DUF4921 DUF4931 GalP_UDP_tr_C GalP_UDP_transf HIT


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Curation and family details

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Seed source: Prosite
Previous IDs: none
Type: Domain
Author: Finn RD, Bateman A, Griffiths-Jones SR
Number in seed: 78
Number in full: 1674
Average length of the domain: 171.60 aa
Average identity of full alignment: 25 %
Average coverage of the sequence by the domain: 45.46 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 17690987 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 22.1 22.1
Trusted cut-off 22.1 22.1
Noise cut-off 22.0 21.9
Model length: 184
Family (HMM) version: 20
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Species distribution

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There are 3 interactions for this family. More...

GalP_UDP_tr_C GalP_UDP_tr_C GalP_UDP_transf


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the GalP_UDP_transf domain has been found. There are 22 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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