Polypeptide N-acetylgalactosaminyltransferase 4 (GALNT4)
The protein contains 578 amino acids for an estimated molecular weight of 66666 Da.
Catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, the transfer of an N-acetyl-D-galactosamine residue to a serine or threonine residue on the protein receptor. Has a highest activity toward Muc7, EA2 and Muc2, with a lowest activity than GALNT2. Glycosylates 'Thr-57' of SELPLG. (updated: Sept. 12, 2018)
Protein identification was indicated in the following studies:
- Bryk and co-workers. (2017) Quantitative Analysis of Human Red Blood Cell Proteome. J Proteome Res. 16(8), 2752-2761.
- D'Alessandro and co-workers. (2017) Red blood cell proteomics update: is there more to discover? Blood Transfus. 15(2), 182-187.
Methods
The following articles were analysed to gather the proteome content of erythrocytes.
The gene or protein list provided in the studies were processed using the ID mapping API of Uniprot in September 2018. The number of proteins identified and mapped without ambiguity in these studies is indicated below.
Only Swiss-Prot entries (reviewed) were considered for protein evidence assignation.
| Publication | Identification 1 | Uniprot mapping 2 | Not mapped / Obsolete | TrEMBL | Swiss-Prot |
|---|---|---|---|---|---|
| Goodman (2013) | 2289 (gene list) | 2278 | 53 | 20599 | 2269 |
| Lange (2014) | 1234 | 1234 | 7 | 28 | 1224 |
| Hegedus (2015) | 2638 | 2622 | 0 | 235 | 2387 |
| Wilson (2016) | 1658 | 1528 | 170 | 291 | 1068 |
| d'Alessandro (2017) | 1826 | 1817 | 2 | 0 | 1815 |
| Bryk (2017) | 2090 | 2060 | 10 | 108 | 1942 |
| Chu (2018) | 1853 | 1804 | 55 | 362 | 1387 |
1 as available in the article and/or in supplementary material
2 uniprot mapping returns all protein isoforms as one entry
The compilation of older studies can be retrieved from the Red Blood Cell Collection database.
The data and differentiation stages presented below come from the proteomic study and analysis performed by our partners of the GReX consortium, more details are available in their published work.
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| Variant | Description |
|---|---|
| dbSNP:rs17853610 | |
| dbSNP:rs2230281 | |
| dbSNP:rs2230283 |
Biological Process
O-glycan processing
Protein O-linked glycosylation via serine
Protein O-linked glycosylation via threonine
The reference OMIM entry for this protein is 603565
Udp-n-acetyl-alpha-d-galactosamine:polypeptide n-acetylgalactosaminyltransferase 4; galnt4
Galnac transferase 4; galnact4
CLONING
Members of the UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase (GalNAcT; EC 2.4.1.41) family control the initiation of mucin-type O-linked protein glycosylation, in which N-acetylgalactosamine (GalNAc) is transferred to serine and threonine amino acid residues. In cancer cells, the reduction in O-glycosylation of MUC1 (158340) leads to the exposure of cancer-associated peptide epitopes within the tandem repeat region of MUC1. In vitro, purified recombinant GalNAcT1 (602273), GalNAcT2 (602274), and GalNAcT3 (601756) glycosylate only 3 of the 5 potential O-glycosylation sites in the MUC1 tandem repeat. To identify additional GalNAcTs which might have substrate specificity for the last 2 sites in the MUC1 repeat, Bennett et al. (1998) used a cDNA sequence that had been previously isolated by RT-PCR using degenerate primers based on sequences flanking a putative GalNAcT motif (Bennett et al., 1996). They isolated cDNAs and genomic clones encoding GalNAcT4. Sequence analysis indicated that the deduced 578-amino acid GalNAcT4 protein is a type II transmembrane protein with a C-terminal region similar to those of other members of the GalNAcT family. GalNAcT4 contains a hydrophobic retention signal predicted to provide retention in the Golgi. Immunofluorescence showed that GalNAcT4 has a Golgi-like localization pattern in salivary glands. In vitro, recombinant GalNAcT4 complemented GalNAcT1, GalNAcT2, and GalNAcT3 in O-glycosylation of the MUC1 tandem repeat by transferring GalNAc to the 2 sites in the MUC1 repeat not utilized by these GalNAcTs. Bennett et al. (1998) suggested that each GalNAcT has distinct functions and that the large size of the GalNACT gene family has evolved as a consequence of the need for O-glycosylation of different protein sequences. Northern blot analysis revealed that the approximately 6-kb GalNAcT4 mRNA is expressed ubiquitously in human adult and fetal tissues.GENE STRUCTURE
Bennett et al. (1998) found that unlike the coding regions of GalNAcT1, GalNAcT2, and GalNAcT3, the entire coding region of GalNAcT4 is contained within 1 exon.MAPPING
By fluorescence in situ hybridization and by linkage analysis, Bennett et al. (1998) mapped the GALNT4 gene to 12q21.3-q22. ... More on the omim web site
June 30, 2020: Protein entry updated
Automatic update: OMIM entry 603565 was added.
Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).