Expression of the long arm sequence of mouse laminin alpha1, beta1, or gamma1 chain in COS1 cells and assembly of monkey-mouse hybrid laminin.

Mouse laminin alpha1, beta1, or gamma1 sequence covering truncated regions of the long arm was transiently expressed in monkey COS1 cells. Unlike natural laminins, in which only alpha beta gamma trimers are selectively assembled and disulfide-bonded at the long arm, a large fraction of mouse chains formed disulfide-bonded homopolymers. However, a small fraction of mouse beta1 (or gamma1) formed hybrid beta1gamma1 dimers with endogenous monkey gamma1 (or beta1). These hybrid beta1gamma1 dimers formed alpha1 beta1 gamma1 trimer with monkey alpha1. Mouse alpha1 also formed disulfide bonds with monkey beta1gamma1 dimer. Thus, a common mechanism is shared by laminin chains of different animal origins. Sequences in the E8 region at the C-terminal end of the long arm were crucial for this chain-selective assembly. When the C-terminal sequence of mouse beta1 long arm was extended beyond the alpha-loop, the hybrid trimer formation was diminished. This supported the model of altered chain arrangement around the alpha-loop.