Co-assembly of Envoplakin and Periplakin into Oligomers and Ca2+-dependent Vesicle Binding

Abstract

Plakin family members envoplakin and periplakin have been shown to be part of the cornified cell envelope in terminally differentiating stratified squamous epithelia. In the present study, purified recombinant human envoplakin and periplakin were used to investigate their properties and interactions. We found that envoplakin was insoluble at physiological conditions in vitro, and co-assembly with periplakin was required for its solubility. Envoplakin and periplakin formed soluble complexes with equimolar stoichiometry. Chemical cross-linking revealed that the major soluble form of all periplakin constructs and of envoplakin/periplakin rod domains was a dimer, although co-assembly of the fulllength proteins resulted in formation of higher order oligomers. Electron microscopy of rotary-shadowed periplakin demonstrated thin flexible molecules with an average contour length of 88 nm for the rod-plus-tail fragment, and immunolabeling EM confirmed the molecule as a parallel, in-register, dimer. Both periplakin and envoplakin/periplakin oligomers were able to bind synthetic lipid vesicles whose composition mimicked the cytoplasmic side of the plasma membrane of eukaryotic cells. This binding was dependent on anionic phospholipids and Ca 2؉ . These findings raise the possibility that envoplakin and periplakin bind to the plasma membrane upon elevation of intracellular [Ca 2؉ ] in differentiating keratinocytes, where they serve as a scaffold for cornified cell envelope assembly.

Forkhead Box C1 Regulates Human Primary Keratinocyte Terminal Differentiation

“…Among the top 50 most significantly differentially expressed genes across the four experimental groups (False discovery rate <0.01), 42 genes were down-regulated in FOXC1 silenced differentiated KC (Fig 4B), including KC terminal differentiation markers of periplakin (PPL)[12], keratinocyte proline-rich protein (KPRP)[13] and Epsin 3 (EPN3)[14], lipids synthesis genes of serine palmitoyltransferase (SPTSSB) and sphingomyelin phosphodiesterase 3 (SMPD3) and FLG maturation related protease gene caspase 14 (CASP14)[15–17]. Additionally, the majority of genes located at epidermal differentiation complex (EDC) of 1p21 [18]were decreased in differentiated KC upon FOXC1 silencing (Table 1).…”

Targeted Proteolysis of Plectin Isoform 1a Accounts for Hemidesmosome Dysfunction in Mice Mimicking the Dominant Skin Blistering Disease EBS-Ogna

“…Whether other cytolinker proteins structurally related to plectin are capable of lateral association as well, and whether plectin can form hetero-oligomers with other cytolinker proteins remains to be shown. Hetero-oligomer formation has previously been observed in the case of periplakin and envoplakin [57], while desmoplakin has been reported to assemble exclusively into dimers [58].…”

Deconstructing the skin: cytoarchitectural determinants of epidermal morphogenesis

“…In addition to these components, specialized plakin proteins, called envoplakin and periplakin, and the secreted desmosomal protein corneodesmosin (CDSN) are incorporated into the cornified envelope 2,163,164 . Envoplakin and periplakin are intermediate- filament-binding proteins that localize to desmosomes in the upper layers, where they are thought to integrate the keratin cytoskeletons of the stratum corneum 165,166 .…”