Molecular Structure of a New Member of the Plectin Family and Gene Expression

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We recently described an individual with subepidermal blistering disease that resembled bullous pemphigoid both clinically and pathologically. Immunoblot analysis revealed that the patient's serum did not react with the 230-or 180-kDa bullous pemphigoid antigens, but recognized exclusively a 450-kDa epidermal polypeptide. To elucidate the molecular structure of this antigen, we have now cloned and characterized the cDNAs encoding a portion of this antigen. We have identified cDNAs encoding plectin and a plectin-like molecule on screening human keratinocyte and HeLa cell cDNA libraries with a probe derived from the immunoreactive clone originally detected by the patient's serum. Epitope mapping showed that the 450-kDa epidermal autoantigen was found to be the plectin-like molecule (sequence G-F). This molecule was named plectin 2. It has a carboxyl terminal domain that contains three highly homologous repeats of 534 amino acids, which differ from human or rat plectin. Similar structure is found in desmoplakin. In this part, another splicig variant existed. It also shows little homology to human bullous pemphigoid antigen 1. These structural difference may have important consequences for biological function. Phosphorylation of the plectin-like molecule at one or more of the many potential sites detected might play an important role in modulating interaction of the protein with cytoskeletal or hemidesmosomal elements.