Filaggrin
keratohyalin granule
Characterization of the human epidermal profilaggrin gene. Genomic organization and identification of an S-100-like calcium binding domain at the amino terminus.
Filaggrin is an intermediate filament-associated protein which functions to aggregate keratin intermediate filaments in the stratum corneum of mammalian epidermis. It is synthesized as a large precursor protein, profilaggrin, that consists of multiple filaggrin units and is localized in keratohyalin granules. In this report, we describe the characterization of cosmid genomic clones containing the human profilaggrin gene coding for 11 complete filaggrin repeats of 324 amino acids each. At the amino- and carboxyl-terminal ends of human profilaggrin are leader and tail peptide sequences of 293 and 157 amino acids, respectively, which differ from filaggrin. The leader peptide is composed of two distinct domains: an 81-residue segment which shows significant homology to the S-100 family of EF hand-containing calcium-binding proteins, and a hydrophilic second domain of 212 residues. The gene is divided into three exons, with one intron (approximately 9.6 kilobase pairs) in the 5' noncoding region and a second one of 570 base pairs between the EF hands. The position of intron 2 is identical to that of other members of the S-100-like family. The presence of an S-100-like domain suggests that profilaggrin binds calcium and that the calcium binding domain is functionally significant in the formation of keratohyalin and/or the subsequent processing of profilaggrin to filaggrin, both of which may be calcium-dependent events.