Cell-cell junctions formed by the cadherin family of calcium-dependent adhesion proteins are fundamental to development and organization of tissues in all multicellular animals. Cadherins are single pass transmembrane proteins which bind to themselves through antiparallel dimers that ultimately connect neighboring cells through their ectodomains. Our goal is to investigate how these cadherins bind to each other and form large junctions using Drosophila neuronal cadherin as a basis, since we can relate structure to function in the model organism. We determined the adhesive region in the large ectodomain through biophysical and structural studies and identified four hydrophobic amino acids in the interface for which mutation to charged residues is predicted to ablate cadherin dimerization. In this study, we expressed and purified DN-cadherin fragments containing these mutations, singly or in combination, from mammalian cells to determine the optimal mutations to fully ablate adhesive binding of DN-cadherin in fly studies. We are testing for loss of binding on molecular level through size exclusion chromatography coupled with multi-angle-light scattering and use a junction reconstitution system to test for loss of binding on membranes. The results will identify amino acids that are crucial for protein binding in the fragments, which will be confirmed in the full-length protein, before ultimately testing the impact of loss of binding in flies. Analogous mutations will be tested in DE-cadherin. This approach will allow us to identify how proteins bind to each other and the roles these cadherins play during development.