Interaction of periplakin and envoplakin with intermediate filaments

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Abstract
Periplakin is a component of desmosomes and the epidermal cornified envelope. Its N-terminal domain interacts with the plasma membrane; it heterodimerises with envoplakin via its rod domain; and its C-terminus interacts with intermediate filaments. Periplakin has the shortest C-terminus of the plakin family, comprising only the linker domain found in all conventional plakins. By transient transfection of COS7 cells and primary human epidermal keratinocytes with deletion mutants of the periplakin C-terminus we mapped sequences required for intermediate filament interaction to two regions of the linker motif that are most highly conserved amongst the plakins. The results were confirmed by overlay assays of the binding of in vitro translated periplakin constructs to keratins and vimentin. We found that envoplakin and periplakin could still associate with each other when parts of their rod domains were deleted and, surprisingly, that removal of the entire rod domain did not completely inhibit their interaction. Co-transfection of constructs containing the C-termini of envoplakin and periplakin suggested that the periplakin C-terminus may stabilise the interaction of the envoplakin C-terminus with intermediate filaments. We conclude that the periplakin C-terminus plays an important role in linking periplakin and envoplakin to intermediate filaments.