Homoâoligomer formation by basigin, an immunoglobulin superfamily member, via its Nâterminal immunoglobulin domain
2000
Yoshida, Seiya | Shibata, Maki | Yamamoto, Satoshi | Hagihara, Masako | Asai, Naoya | Takahashi, Masahide | Mizutani, Shigehiko | Muramatsu, Takashi | Kadomatsu, Kenji
Basigin (Bsg) is a highly glycosylated transmembrane protein with two immunoglobulin (Ig)âlike domains. A number of studies, including gene targeting, have demonstrated that Bsg plays pivotal roles in spermatogenesis, implantation, neural network formation and tumor progression. In the present study, to understand the mechanism of action of Bsg, we determined its expression status on the plasma membrane. Cotransfection of Bsg expression vectors with two different tags clarified that Bsg forms homoâoligomers in a cisâdependent manner on the plasma membrane. If the disulfide bond of the more Nâterminally located Igâlike domain was destroyed by mutations, Bsg could not form oligomers. In contrast, the mutations of the Câterminal Igâlike domain or Nâglycosylation sites did not affect the association. The association of mouse and human Bsgs, which exhibit high homology in the transmembrane and intracellular domains but low homology in the extracellular domain, was very weak as compared with that within the same species, suggesting the importance of the extracellular domain in the association. If the extracellular domain of the human Ret protein was replaced with the Nâterminal Igâlike domain of Bsg, the resulting chimera protein was associated with intact wildâtype Bsg, but not if the Câterminal Igâlike domain, instead of the Nâterminal one, of Bsg was used. No oligomer formation took place between the intact wildâtype Ret and Bsg proteins. In conclusion, these data indicate that the Nâterminal Igâlike domain is necessary and sufficient for oligomer formation by Bsg on the plasma membrane.
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