Laminin chain assembly. Specific sequences at the C terminus of the long arm are required for the formation of specific double- and triple-stranded coiled-coil structures.

The assembly of laminin chains into double- and triple-stranded structures was studied with recombinant proteins derived from the C-terminal alpha-helical region of the long arm of laminin. Both affinity assays and structural studies demonstrated chain-specific assembly of the B1, B2, and A chains, while associations between homotypic and homologous chains could not be observed. These results suggest that chain selection is controlled by the C-terminal region. Deletion mapping in the B1e and B2e chains identified two sites important for dimer and trimer formation. These two sites were separated by 23 amino acids in the B1e chain, whereas they were adjacent in the B2e chain. The Ae and Am chains contained only one site for trimerization. Site-directed mutagenesis revealed that charged amino acid residues within these sites were essential for association. These results suggest that distinct sites within the C-terminal alpha-helical region of the laminin long arm are critical for the chain-specific assembly of these macro-molecules.