Desmoyokin, a 680 kDa keratinocyte plasma membrane-associated protein, is homologous to the protein encoded by human gene AHNAK

We have obtained a monoclonal antibody (33A-3D) that specifically recognize desmoyokin, a 680 kDa desmosomal plaque protein that is well characterized in bovine muzzle epidermis. A cDNA clone (DY6, 3693 bp) was isolated by immunoscreening a mouse keratinocyte expression library with 33A-3D, and it was confirmed that DY6 has a partial coding sequence for desmoyokin. DY6 consists of highly homologous repeats about 128 residues long. Furthermore, the 128-residue repeats exhibit a quasi seven-residue substructure, which we believe will adopt an antiparallel β-sheet structure. Surprisingly, the amino acid sequence showed a significant homology with AHNAK, a newly identified human gene encoding a 700 kDa protein, which was suggested to be down-regulated in neuroblastoma. From its extensive homology, the similarity in both size and structure, and the identical patterns on Southern blot analysis of genomic DNAs, desmoyokin and AHNAK protein are thought to be identical. Although the desmoyokin/AHNAK protein is detected in a variety of cell types at both protein and mRNA levels, its distribution in keratinocytes (associated closely with cell membrane) is quite different from that in cells other than keratinocytes (distributed diffusely in the cytoplasm). These findings suggest that the desmoyokin/AHNAK protein is a ubiquitous molecule with a unique structure and appears to have different distributions (and probably different functions) among different cells.