The complete cDNA and deduced amino acid sequence of a type II mouse epidermal keratin of 60,000 Da: analysis of sequence differences between type I and type II keratins.

Abstract

The complete nucleotide and deduced amino acid sequences of a mouse epidermal keratin subunit of 60,000 Da [daltons] are presented. The keratin possesses a central .alpha.-helical domain of 4 tracts (termed 1A, 1B, 2A and 2B) that can form coiled-coils, interspersed by short linker sequences, and has non-.alpha.-helical terminal domains. This pattern of secondary structure is emerging as common to all intermediate filament subunits. The .alpha.-helical sequences conform to the type II class of keratins. Accordingly, this is the 1st type II keratin for which complete sequence information is available, and it facilitates elucidation of the fundamental distinctions between type I and type II keratins. Type I keratins are acidic and type II keratins are neutral-basic in charge. The basis for this empirical correlation between type and charge resides in the respective net charges of the 1A and 2B tracts. Calculations on interchain interactions between charged residues in the .alpha.-helical domains indicate that this keratin prefers to participate in dimers according to an in-register parallel arrangement. The terminal domains of this keratin possess characteristic Gly-rich sequences, and the carboxyl-terminal domain is highly homologous to that of a human epidermal keratin of 56,000 Da. According to the hypothesis that end-domains are located on the periphery of keratin filaments, the corresponding mouse and human keratins are closely related, both structurally and functionally.