Trichohyalin-like protein 1 (TCHHL1) is a member of the fused-type S100 protein family. It contains an N-terminal E-hand domain, one trans-membrane domain and a nuclear localization signal. Its function is not clear. It is expressed in the basal layer of the normal epidermis and may be associated with the proliferation of keratinocytes [].The fused-type S100 protein family is a group of calcium binding S100-related proteins. The 'fused' gene family includes multifunctional epidermal differentiation proteins - profilaggrin, trichohyalin, repetin [], hornerin, and cornulin; functionally these proteins are associated with keratin intermediate filaments and partially crosslinked to the cell envelope. These 'fused' gene proteins contain N-terminal sequence with two Ca-binding EF-hands motif, which may be associated with calcium signalling in epidermal cells and autoprocessing in a calcium-dependent manner. In contrast to S100 proteins, 'fused' gene family proteins contain an extraordinary high number of almost perfect peptide repeats with regular array of polar and charged residues similar to many known cell envelope proteins [].
