H-1, N-15 and C-13 resonance assignments and monomeric structure of the amino-terminal extracellular domain of epithelial cadherin

E-cadherin is a transmembrane protein that provides Ca2+-dependent cell adhesion to epithelial cells. The large majority of the H-1, N-15, C-13 and (CO)-C-13 resonances of a 146-amino acid polypeptide from epithelial (E-) cadherin have been assigned using multidimensional NMR spectroscopy. The structure of the amino-terminal 100 amino acids, corresponding to the first extracellular repeat of E-cadherin [Overduin et al. (1995) Science, 267, 386-389], has been refined. The monomeric state of this isolated domain is demonstrated by light scattering and sedimentation analysis. Seven beta-strands and two short helices were identified by patterns of NOE cross-beaks, vicinal coupling constants and chemical shift indices. A novel structural motif termed a quasi-beta-helix found in the crystal structure of a neural (N-) cadherin domain [Shapiro et al. (1995) Nature, 374, 327-337] is characterized in detail for the first time by NMR. Slowly exchanging amides were concentrated in the beta-sheet region and quasi-beta-helix. The beta-barrel fold of the cadherin domain is topologically similar to the immunoglobulin fold. Comparison of this solution structure to the crystallized dimers of the N-terminal pair of E-cadherin domains [Nagar et al. (1996) Nature, 380, 360-364] and of the homologous single domain of N-cadherin reveals a conserved cadherin fold with minor structural differences, which can be accounted forby differences in metal ligation and oligomeric state.