New arrangement of proteins and lipids in the stratum corneum cornified envelope

A new arrangement of proteins and lipids of stratum corneum (SC) cornified envelope (CE) is proposed. The chemical analysis of CE revealed the presence of free fatty acids (FFA), ceramides (Cer), and important percentages of glutamic acid/glutamine (Glx) and serine (Ser) residues. The molecular structure of these components suggests the existence of covalent links not only between Cer and Glx but also between FFA and Ser. The protein distribution of extracellular surface of CE, i.e., the proteins that could be involved in the bonds with lipids, was studied using post- and pre-embedding immunolabeling electron microscopy. Some loricrin (protein rich in Ser) was detected in the outermost part of the CE protein layer. The external arrangement of some domains of this protein may give rise to form linkages with FFA, yielding further insight into the CE arrangement in which Cer–Glx bonds and FFA–Ser bonds would be involved. Although the importance of fatty acids in the cohesion and barrier function of SC has been widely demonstrated, their role could be associated not only to the presence of these lipids in the intercellular lamellae but also in the CE, in the same way that Cer.