Several tetraspanins bind directly to a few molecular partners to form primary complexes, which might assemble through tetraspanin–tetraspanin interactions to form a network of molecular interactions, the tetraspanin web. We have produced a monoclonal antibody directed to a 63 kDa molecule (determined under non-reducing conditions) associated with CD9. This molecule was first identified by MS as a molecule with four Ig domains, EWI-2. Like the related molecule CD9P-1, EWI-2 was found to be a partner not only for CD9, but also for CD81, a tetraspanin required for hepatic infection by the parasite responsible for malaria, and also a putative hepatitis C virus receptor. Using chimaeric CD9/CD82 molecules, two separate regions of CD9 of 40 and 47 amino acids were demonstrated to confer the ability to interact with EWI-2. Both EWI-2 and CD9P-1 were detected in the human liver at the surface of hepatocytes and were found to associate with CD81 on freshly isolated hepatocytes. EWI-2 also co-localized with CD81 in the liver. CD9P-1 was not detected on most peripheral blood cells, whereas EWI-2 was expressed on the majority of B-, T- and natural killer cells and was not detected on monocytes, polynuclear cells or platelets. This distribution is identical to that of CD81. Finally, EWI-2 associated with all tetraspanins studied after lysis under conditions preserving tetraspanin–tetraspanin interactions, showing that EWI-2 is a new component of the tetraspanin web.
- tetraspanin web
The nucleotide sequence data for clone Bx19c11 was deposited in the GenBank® EMBL, DDBJ and GSDB Nucleotide Sequence Databases under accession number AY044845.
Abbreviations used: mAb, monoclonal antibody; IgSF, immunoglobulin superfamily; TM, transmembrane; LEL, large extracellular loop; PGF2α, prostaglandin F2α; HCV, hepatitis C virus; MALDI-TOF, matrix-assisted laser-desorption ionization–time-of-flight; DSP, dithiobis(succinimidyl propionate); NK cells, natural killer cells; CHO cells, Chinese hamster ovary cells; PE, phycoerythrin.
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