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8.A.40.1.1
CD81 (TAPA1, Tspan28) co-receptor of Hepatitis C Virus (HCV); 236 aas; it forms a heterodimer with SR-B1 (TC#9.B.39.1.3). Defects cause CVID6. It plays a role in hepatitis C entry via endocytosis (Farquhar et al., 2011), and also plays roles in immune and other physiological functions (Yeh and Klesius 2009).  Sperm-egg interaction and fusion would not happen in mammals without tetraspanin superfamily members including protein CD81 (Jankovicova et al. 2016). Abnormal levels occur in plasma neuron-derived extracellular vesicles of early schizophrenia and other neurodevelopmental diseases (Goetzl et al. 2022).  Tetraspanin CD81 serves as a functional entry factor for porcine circovirus type 2 infection (Li et al. 2025).

Accession Number:P60033
Protein Name:CD81 antigen
Length:236
Molecular Weight:25809.00
Species:Homo sapiens (Human) [9606]
Number of TMSs:4
Location1 / Topology2 / Orientation3: Membrane1 / Multi-pass membrane protein2
Substrate

Cross database links:

Entrez Gene ID: 975   
Pfam: PF00335   
KEGG: hsa:975   

Gene Ontology

GO:0005887 C:integral to plasma membrane
GO:0005515 F:protein binding
GO:0000187 P:activation of MAPK activity
GO:0008283 P:cell proliferation
GO:0006661 P:phosphatidylinositol biosynthetic process
GO:0043128 P:positive regulation of 1-phosphatidylinositol 4-kinase activity
GO:0008284 P:positive regulation of cell proliferation
GO:0050731 P:positive regulation of peptidyl-tyrosine phosphorylation
GO:0008104 P:protein localization
GO:0050776 P:regulation of immune response
GO:0046813 P:virion attachment, binding of host cell surface receptor

References (11)

[1] “TAPA-1, the target of an antiproliferative antibody, defines a new family of transmembrane proteins.”  Oren R.et.al.   1695320
[2] “Human chromosome 11 DNA sequence and analysis including novel gene identification.”  Taylor T.D.et.al.   16554811
[3] “The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).”  The MGC Project Teamet.al.   15489334
[4] “Structure and membrane topology of TAPA-1.”  Levy S.et.al.   1860863
[5] “EWI-2 is a major CD9 and CD81 partner and member of a novel Ig protein subfamily.”  Stipp C.S.et.al.   11504738
[6] “CD81-dependent binding of hepatitis C virus E1E2 heterodimers.”  Cocquerel L.et.al.   12970454
[7] “Cell entry of hepatitis C virus requires a set of co-receptors that include the CD81 tetraspanin and the SR-B1 scavenger receptor.”  Bartosch B.et.al.   12913001
[8] “CD81 gene defect in humans disrupts CD19 complex formation and leads to antibody deficiency.”  van Zelm M.C.et.al.   20237408
[9] “Initial characterization of the human central proteome.”  Burkard T.R.et.al.   21269460
[10] “CD81 extracellular domain 3D structure: insight into the tetraspanin superfamily structural motifs.”  Kitadokoro K.et.al.   11226150
[11] “Subunit association and conformational flexibility in the head subdomain of human CD81 large extracellular loop.”  Kitadokoro K.et.al.   12437138
Structure:
1G8Q   1IV5   3X0E   5DFV   5DFW   5tcx   5M2C   5M33   5M3D   5M3T   [...more]

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FASTA formatted sequence 
1:	MGVEGCTKCI KYLLFVFNFV FWLAGGVILG VALWLRHDPQ TTNLLYLELG DKPAPNTFYV 
61:	GIYILIAVGA VMMFVGFLGC YGAIQESQCL LGTFFTCLVI LFACEVAAGI WGFVNKDQIA 
121:	KDVKQFYDQA LQQAVVDDDA NNAKAVVKTF HETLDCCGSS TLTALTTSVL KNNLCPSGSN 
181:	IISNLFKEDC HQKIDDLFSG KLYLIGIAAI VVAVIMIFEM ILSMVLCCGI RNSSVY