Background: Epidermal keratinization involves various post-translational modifications including the deimination of arginine residues. Major deiminated proteins are derived from keratin K1. Two preferred deimination sites were identified in the V subdomain of mouse K1. An antibody against one of the deiminated peptide sequences (ACP) recognized deiminated mouse and human K1, and stained the cornified layers of human and infant mouse epidermis. ACP also stained the outermost layer of mouse embryonic epidermis. Western blotting revealed minor proteins showing strong ACP-positive signals in the mouse embryonic epidermal extract in which deiminated K1 derivatives were hardly detected.
Objective: To characterize ACP-positive proteins expressed in mouse embryonic epidermis.
Methods: ACP-positive proteins were isolated by preparative gel electrophoresis for N-terminal sequencing followed by blast searches for matching sequences in the protein and nucleotide database.
Results: We obtained N-terminal sequences of two ACP-positive proteins. A cDNA clone in the est_mouse database has an open reading frame for 202 amino acid residues containing both sequenced peptides. The deduced sequence shows typical features of the N-terminal portion of type II keratins. A virtually identical sequence to this reading frame is present in a genomic contig of chromosome 15 on which keratin type II genes are clustered. Sequential searches for overlapping cDNA clones in the est_mouse database along with similar searches in the genomic contig formulated a hypothetical cDNA sequence encoding a putative protein of 572 amino acid residues tentatively called K1-emb.
Conclusion: We predicted a sequence of novel type II keratin site-specifically deiminated in embryonic mouse epidermis.