Glycoprotein Xg (XG)
The protein contains 180 amino acids for an estimated molecular weight of 19723 Da.
No function (updated: Sept. 12, 2018)
Protein identification was indicated in the following studies:
- Hegedűs and co-workers. (2015) Inconsistencies in the red blood cell membrane proteome analysis: generation of a database for research and diagnostic applications. Database (Oxford) 1-8.
- Bryk and co-workers. (2017) Quantitative Analysis of Human Red Blood Cell Proteome. J Proteome Res. 16(8), 2752-2761.
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.
This protein is annotated as membranous in UniProt, is predicted to be membranous by TOPCONS.
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| Variant | Description |
|---|---|
| dbSNP:rs5939319 |
No binding partner found
Biological Process
Homotypic cell-cell adhesion
Positive regulation of neutrophil extravasation
T cell extravasation
Molecular Function
The reference OMIM entry for this protein is 300879
Xg glycoprotein; xg
Pbdx
CLONING
Ellis et al. (1994) identified XG, which they called PBDX, as the gene encoding the Xg(a) antigen of the XG blood group (314700). Using rabbit polyclonal and mouse monoclonal antibodies raised against a peptide derived from the N-terminal domain of the predicted mature PBDX protein, they identified the Xg(a) antigen. By its identity with PBDX, therefore, Xg(a) was recognized as a cell-surface antigen 48% homologous to CD99 (313470), which is encoded in the tightly linked MIC2 gene. Northern blot and RT-PCR analyses detected PBDX expression in hematopoietic tissues, including umbilical cord, adult bone marrow, and fetal liver, thymus, and spleen, as well as in cultured skin fibroblasts. Expression was low or undetectable in all other tissues and cell lines examined. Immunoblot analysis using anti-Xg(a) as probe detected bands with apparent molecular masses from 24 to 29 kD in membrane lysates from Xg(a)-positive, but not Xg(a)-negative, erythrocytes. By Northern blot analysis of human tissues, Fouchet et al. (2000) detected major XG transcripts of 2.3 and 1.0 kb and a minor transcript of 3.8 kb in erythroid tissues, including thymus, bone marrow, and fetal liver, and several nonerythroid tissues, including heart, placenta, skeletal muscle, prostate, thyroid, spinal cord, and trachea. RT-PCR also detected XG expression in adult lung, kidney, and testis and in fetal spleen, adrenal gland, brain, pancreas, and small intestine. Western blot analysis of human erythrocytes, transfected mouse cells, and somatic hybrids revealed a 26-kD XG protein.GENE FUNCTION
Goodfellow et al. (1987) presented evidence suggesting the existence of a pseudoautosomal locus, XGR (314705), that regulates expression of MIC2 and XG. Ellis et al. (1994) concluded that the XG polymorphism of the XG blood group system is defined by a difference in the level of the Xg antigen on the surface of the erythrocyte rather than a difference in the amino acid sequences of the protein products encoded by the Xg(a) allele and an alternative Xg(a)-negative allele. They proposed a model in which the observed XG polymorphism may be due to variation in XGR, which may be situated between the XG locus proximally and the MIC2 locus distally. Using flow cytometry and Western and Northern blot analyses, Fouchet et al. (2000) provided a quantitative estimation of XG and CD99 on human erythrocytes. Their findings supported the hypothesis of genetic control of XG and CD99 expression by the hypothetical XGR locus. Fouchet et al. (2000) examined coexpression of human XG and CD99 cDNAs in transfected mouse cells, either in double transfectants or in somatic hybrids from single transfectants. Their findings were consistent with transcriptional coregulation of XG and CD99 expression, because no influence of either protein on the surface production of the other was observed. In addition, Fouchet et al. (2000) found no evidence of association or complex formation between XG and CD99 on transfected mouse cells or human erythrocytes.GENE STRUCTURE
In her review of the XG blood group system, Johnson (2011) stated that the XG gene contains 10 exons.MAPPING
In her review of the XG blood group system, Johnson (2011) stated that the XG gene spans the pseudoautosomal boundary between the 2 regions of the X chromosome at Xp22.3; exons 1 to 3 are located in the pseudoautosomal region, and exons 4 to 10 are located in the sex chromosome-specific region. Th ... More on the omim web site
Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).
Oct. 19, 2018: Protein entry updated
Automatic update: OMIM entry 300879 was added.