Aggregates keratin intermediate filaments and promotes disulfide-bond formation among the intermediate filaments during terminal differentiation of mammalian epidermis. In the stratum granulosum of the epidermis, localized within keratohyalin granules. In granular keratinocytes and in lower corneocytes, colocalizes with calpain-1/CAPN1 (By similarity). Expressed in the granular layer of the epidermis (at protein level) (PubMed:3680218, PubMed:6174530). Expressed in the epidermis of the ear (at protein level) (PubMed:24751727). Filaggrin is initially synthesized as a large, insoluble, highly phosphorylated precursor containing many tandem copies of 248 AA, which are not separated by large linker sequences. During terminal differentiation it is dephosphorylated and proteolytically cleaved. Belongs to the S100-fused protein family.