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24  structures 4016  species 3  interactions 4580  sequences 37  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, galactose-1-phosphate uridylyltransferase
External IDs OMIM: 606999 MGI: 95638 HomoloGene: 126 GeneCards: GALT
Gene location (Human)
Chromosome 9 (human)
Chr. Chromosome 9 (human)[1]
Chromosome 9 (human)
Genomic location for GALT
Genomic location for GALT
Band 9p13.3 Start 34,638,133 bp[1]
End 34,651,035 bp[1]
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr 9: 34.64 – 34.65 Mb Chr 9: 41.76 – 41.76 Mb
PubMed search [3] [4]
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.[5]

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.[5]


GALT catalyzes the second reaction of the Leloir pathway of galactose metabolism through ping pong bi-bi kinetics with a double displacement mechanism.[6] This means that the net reaction consists of two reactants and two products (see the 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.[7] 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.[8]

  1. UDP-glucose + E-His ⇌ Glucose-1-phosphate + E-His-UMP
  2. Galactose-1-phosphate + E-His-UMP ⇌ UDP-galactose + E-His[8]
Two-step action of galactose-1-phosphate uridylyltransferase. Image adapted from [9]

Structural studies

The three-dimensional structure at 180 pm resolution (x-ray crystallography) of GALT was determined by Wedekind, Frey, and Rayment, and their structural analysis found key amino acids essential for GALT function.[8] Among these are Leu4, Phe75, Asn77, Asp78, Phe79, and Val108, which are consistent with residues that have been implicated both in point mutation experiments as well as in clinical screening that play a role in human galactosemia.[8][10]

Clinical significance

Deficiency of GALT causes classic galactosemia. Galactosemia is an autosomal recessive inherited disorder detectable in newborns and childhood.[11] It occurs at 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 manifestations, Duarte (D/D) and the Duarte/Classical variant (D/G) are caused by the attenuation of GALT activity.[12] Symptoms include ovarian failure, developmental coordination disorder (difficulty speaking correctly and consistently),[13] and neurologic deficits.[12] A single mutation in any of several base pairs can lead to deficiency in GALT activity.[14] 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.[12] These two mutations also add new restriction enzyme cut sites, which enable detection by and large-scale population screening with PCR (polymerase chain reaction).[12] 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.[11][15] However, those afflicted with galactosemia can live relatively normal lives by avoiding milk products and anything else containing galactose (because it cannot be metabolized), but there is still the potential for problems in neurological development or other complications, even in those who avoid galactose.[16]

Disease database

Galactosemia (GALT) Mutation Database


  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000213930 - Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000036073 - Ensembl, May 2017
  3. ^ "Human PubMed Reference:". 
  4. ^ "Mouse PubMed Reference:". 
  5. ^ a b "Entrez Gene: GALT galactose-1-phosphate uridylyltransferase". 
  6. ^ 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. PMID 4606575. doi:10.1021/bi00716a011. 
  7. ^
  8. ^ 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. PMID 7669762. doi:10.1021/bi00035a010. 
  9. ^
  10. ^ 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. PMID 10220154. doi:10.1002/(SICI)1098-1004(1999)13:4<339::AID-HUMU18>3.0.CO;2-S. 
  11. ^ a b Fridovich-Keil JL (December 2006). "Galactosemia: the good, the bad, and the unknown". J. Cell. Physiol. 209 (3): 701–5. PMID 17001680. doi:10.1002/jcp.20820. 
  12. ^ 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. PMID 7671959. doi:10.1007/BF02143798. 
  13. ^ "Archived copy". Archived from the original on 2006-02-28. Retrieved 2010-05-19. 
  14. ^ 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. PMC 1907369Freely accessible. PMID 12552079. doi:10.1016/S1525-1578(10)60450-3. 
  15. ^ Lai K, Elsas LJ, Wierenga KJ (November 2009). "Galactose toxicity in animals". IUBMB Life. 61 (11): 1063–74. PMC 2788023Freely accessible. PMID 19859980. doi:10.1002/iub.262. 
  16. ^

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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Curation View help on the curation process

Seed source: Prosite
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Finn RD , Bateman A , Griffiths-Jones SR
Number in seed: 76
Number in full: 4580
Average length of the domain: 169.60 aa
Average identity of full alignment: 26 %
Average coverage of the sequence by the domain: 45.63 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -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 22.0
Model length: 184
Family (HMM) version: 22
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Species distribution

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

GalP_UDP_transf GalP_UDP_tr_C GalP_UDP_tr_C


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 24 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 sequence.

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