Disulfide-bonding between Drosophila laminin beta and gamma chains is essential for alpha chain to form alpha betagamma trimer.

Assembly of Drosophila laminin alpha, beta and gamma chains was analyzed by immunoprecipitation of the lysate from metabolically radiolabeled Kc 167 cells with chain-specific antibodies followed by two dimensional electrophoresis in which non-reducing and reducing SDS gel electrophoresis are combined. Precipitation of monomeric beta (or gamma) with anti-gamma (or -beta) antibody revealed that beta and gamma form stable dimer before they are disulfide-bonded to each other. In contrast, alpha associates with neither monomeric beta, monomeric gamma nor betagamma dimer without disulfide-bonding but only with disulfide-bonded betagamma dimer to form alpha betagamma trimers. These results thus demonstrated that the interchain disulfide-boding between beta and gamma is essential for alpha to form alpha betagamma trimer. We also found that the alpha betagamma trimer can be secreted with alpha chain either disulfide-bonded or not bonded to the disulfide-bonded betagamma dimer.