Heterotrimeric configuration is essential to the adhesive function of laminin

Mouse PFHR9 laminin, B1B2-heterodimers, and free B1-chains were separated from one another by gel filtration on Superose 6. The cell attachment promoting activity of these species was measured after immunoprecipitation with monoclonal anti-laminin antibodies coupled to Sepharose 6MB beads. These antibodies, which did not react with the laminin E8 fragment, were directed against epitopes in the NH2-terminus of the laminin B1-chain and in the central region of laminin. After incubation with purified EHS laminin, the immunosorbents revealed efficient adhesion substrates for a rat rhabdomyosarcoma cell line which attached preferentially to the laminin E8 fragment. Although both were immunoprecipitated efficiently, B1B2-heterodimers and B1-chains, unlike PFHR9 laminin, did not support the attachment of RMS cells. On a molar basis B1B2-heterodimers were 24 times less efficient than PFHR9 laminin or EHS laminin in supporting cell attachment. These data suggest that heterotrimeric configuration is essential to the adhesive function of the laminin E8 fragment.