Desmosomal glycoproteins 2 and 3 (desmocollins) show N-terminal similarity to calcium-dependent cell-cell adhesion molecules

The N-terminal sequence of a mixture of desmosomal glycoproteins 2 and 3 (dg2/3, desmocollins) from bovine nasal epidermis, prepared by electro-elution from polyacrylamide gels, was determined by solidphase Edman degradation. A sequence of 23 amino acids was obtained. This showed 43% identity with that of the N terminus of the calcium-dependent cell adhesion molecule, N-cadherin. A lesser degree of identity with other members of the cadherin–uvo– morulin-L-CAM family was also found. In order to confirm that the sequence was derived from the dg2/3 molecules a rabbit antiserum was raised against a synthetic peptide corresponding to the sequence, conjugated to keyhole limpet haemocyanin (KLH). The antiserum obtained showed high (titre) activity against both the peptide and KLH in ELISA. Each activity could be specifically adsorbed with the appropriate ligand. The antiserum reacted specifically with both dg2 and dg3 of bovine nasal epidermis on immunoblots, this binding was blocked by the N-terminal peptide but was unaffected by KLH. The identity of dg2 and -3 in these preparations was confirmed by immunoblotting with two monoclonal antibodies and one polyclonal antiserum raised against the whole molecules. The N-terminal peptide antiserum was shown to bind to the intercellular space of desmosome profiles by immunoelectron microscopy on ultra-thin frozen sections. One of the two monoclonal antibodies (07–4D) also reacted with the desmosomal intercellular space. dg2 and -3 were shown by Staphylococcus aureus V8 protease digestion to have identical one-dimensional peptide maps. Both the N-terminal antiserum and 07–4D reacted with a V8 fragment of 19000Mr derived from dg2 and dg3. The other monoclonal antibody (52–3D), which has previously been shown to react with the cytoplasmic regions of dg2/3, recognised V8 fragments of lower molecular weight. These results indicate that the dg2/3 molecules of epidermal desmosomes are related to a family of calcium-dependent adhesion molecules, demonstrate that the N-termini of the molecules are located extracellularly, and support the view that they are directly implicated in desmosomal adhesion.