GPA33 (glycoprotein A33 (transmembrane))

Alias_names	glycoprotein A33 (transmembrane)
Alias_symbol (synonym)	A33
Other alias	MGC129986
	MGC129987
HGNC (Hugo)	GPA33
LocusID (NCBI)	10223
Atlas_Id	40735
Location	1q24.1  [Link to chromosome band 1q24]
Location_base_pair	Starts at 167052836 and ends at 167090631 bp from pter ( according to hg19-Feb_2009)  [Mapping GPA33.png]

	Genomic organization of the GPA33 gene. Coding exonic sequences appear in red, non-coding exonic sequences are in blue and intronic sequence are in yellow, with the corresponding exon and intron sizes given below in base pairs (bp). The exon numbers are indicated above each exon. Note the GPA33 gene is in on the reverse strand.
Description	The human GPA33 gene comprises 7 exons (all coding) spanning 37,787 bp of genomic DNA.
Transcription	2,793 bp mRNA; 960 bp open reading frame (Heath et al., 1997).

	Schematic representation of the GPA33 protein, indicating the position of the Ig-like V-type and Ig-like C2-type domain in the extracellular region and the polycysteine residue ('CCCC' motif).
Description	319 amino acids; 43 kDa protein. The A33 glycoprotein is a member of the immunoglobulin superfamily and contains three distinct structural domains: a 213 amino acid extracellular region containing two immunoglobulin-like domains (a C2-type domain and a v-type domain), a 23 amino acid hydrophobic transmembrane domain, and a 62 amino acid highly polar intracellular tail containing four consecutive cysteine residues (Heath et al., 1997). Post translational modification includes N-glycosylation (containing approximately 8 kDa of N-linked carbohydrate), and S-palmitoylation. The S-palmitoylation may be involved in regulating the internalization process initiated by binding of the monoclonal antibody A33 to the A33 antigen. There is no evidence of O-glycosylation, sialylation or glycophosphatidylinositol (Ritter et al., 1997).
Expression	GPA33 demonstrates a rare tissue-specific expression pattern. GPA33 is a cell surface differentiation antigen that is constitutively expressed on the basolateral surfaces of normal human and mouse colon and small bowel epithelium. GPA33 is homogeneously expressed in over 95% of both human primary and metastatic colon cancers, and in 55% of gastric carcinomas, although absent in normal stomach epithelium (Welt et al., 1990).
Localisation	Membrane; single-pass type 1 membrane protein.
Function	Unknown; the protein structure is consistent with a putative role of GPA33 in cell-cell recognition and signaling (Heath et al., 1997). A33 may play a role in relaying information between intestinal epithelial cells and the gut immune system (Lee et al., 2007).
Homology	The two Ig-like domains are well conserved between humans, chimpanzee, dog, mouse and rat, whereas chicken and zebrafish retain only the Ig-like V-like domain. The overall GPA33 protein similarity between humans and various species are: chimpanzee (Pan troglodytes) 97%, domestic dog (Canis lupus familiaris) 75%, mouse (Mus musculus) 66%, rat (Rattus norvegicus) 68%, domestic chicken (Gallus gallus) 44%, and zebrafish (Danio rerio) 35%.

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