Epiplakin, a novel member of the plakin family originally identified as a 450-kDa human epidermal autoantigen - Structure and tissue localization

A 450-kDa human epidermal autoantigen was originally identified as a protei n that reacted with the serum from an individual with a subepidermal bliste ring disease. Molecular cloning of this protein has now shown that it conta ins 5065 amino acids and has a molecular mass of 552 kDa. As reported previ ously this protein, which we call epiplakin, belongs to the plakin family, but it has some very unusual features. Epiplakin has 13 domains that are ho mologous to the B domain in the COOH-terminal region of desmoplakin. The la st five of these B domains, together with their associated linker regions, are particularly strongly conserved. However, epiplakin lacks a coiled-coil rod domain and an amino-terminal domain, both of which are found in all ot her known members of the plakin family. Furthermore, no dimerization motif was found in the sequence. Thus, it is likely that epiplakin exists in vivo as a single-chain structure. Epitope mapping experiments showed that the o riginal patient's serum recognized a sequence unique to epiplakin, which wa s not found in plectin. Immunofluorescence staining revealed the presence o f epiplakin in whole sheets: of epidermis and esophagus, in glandular cells of eccrine sweat and parotid glands and in mucous epithelial cells in the stomach and colon.