Transglutaminase-mediated cross-linking in mammalian epidermis.

The epsilon-(gamma-glutamyl)lysine isopeptide bond has been identified in certain structural proteins of the hair fibre and the epidermis. The major cross-linked proteins are not keratins and generally have little or no cysteine, but have a high glutamic acid/glutamine residue content. In the hair fibre the cross-link appears in the citrulline-containing proteins of the medulla and the inner root sheath of the follicle. In the epidermis the cross-linked proteins are involved in the formation of the cornified envelope of the stratum corneum cells. In both cases, the cross-linked proteins contribute the characteristic property of chemical resistance to their biological structures.