Mutation analysis of cadherin-4 reveals amino acid residues of EC1 important for the structure and function

To clarify the structural basis of the cell adhesion activity of cadherins, we examined the effects of point mutations of well-conserved amino acid re sidues in the extracellular domain 1 of cadherin-4 (Cdh4) on the adhesion p roperties by alanine scanning mutagenesis. Mutations of two web-conserved a romatic amino acid residues in the extracellular domain 1 resulted in abnor mal processing of Cdh4 molecules and no cell adhesion activity, whereas mut ations of the corresponding aromatic amino acids in the extracellular domai n 2 did not show these effects, suggesting a role for the two residues in t he extracellular domain 1 in the folding and/or intracellular transport pro cesses of Cdh4. Mutations of the amino acid residues suspected to be involv ed in strand dimer formation resulted in loss or significant decrease in ce ll adhesion activity. The mutant Cdh4s showed weak concentration at cell-ce ll adhesion sites and chemical cross-linking suggested that the strand dime r formation was actually impaired in the mutants. These results are consist ent with the zipper model, in which the extracellular domain 1 of Cdh4 has intrinsic strand dimer formation activity in addition to adhesion dimer for mation activity, both of which are involved in cell adhesion activity. The zipper model, however, needs further improvement to fully account for the p resent results. (C) 2000 Academic Press.