Purification and characterization of a basic protein from the stratum corneum of mammalian epidermis

A basic protein has been isolated and purified from the stratum corneum of newborn rat epidermis. This protein is referred to as stratum corneum basic protein. It was purified by ion-exchange chromatography on DE-52 and CM-52 cellulose. The protein has a molecular weight of 50 000 on sodium dodecyl sulfate-polyacrylamide gels. It is composed of one polypeptide chain and contains no detectable carbohydrate. The protein has an isoelectric point in the range of pH 9-10, but decomposes during isoelectric focusing giving rise to a polypeptide of less than 10 000 daltons. Amino acid analysis reveals high quantities of glutamic acid, glycine, serine, arginine and relatively high levels of histidine, with these five amino acids composing 74% of the total residues. The amino acid analysis is very similar to histidine-containing keratohyalin proteins isolated from the granular layer of epidermis by several investigators. The stratum corneum basic protein differs from fibrous proteins isolated from the same cell layer with respect to net charge, amino acid composition, and molecular weight. The protein does not react with antibody to the fibrous protein. The basic protein has properties which are consistent with its possible function as a stratum corneum interfilamentous matrix protein.