Characterization of a phosphorylated form of the intermediate filament-aggregating protein filaggrin.
Filaggrin and a phosphorylated form of filaggrin, which has been shown by pulse-chase studies to be a precursor form of the protein [Dale, B. A., & Ling, S. Y. (1979) Biochemistry 18, 3539-3546], were compared for functional, biochemical, and physical properties. Filaggrin reacts with keratin filaments to form visible macrofibrils, unlike the precursor which does not. Biochemical and peptide-mapping studies suggest that the two proteins have similar, perhaps identical, amino acid sequences. The major differences between the two proteins are in molecular weight (precursor, 44 200 g/mol; filaggrin, 38 400 g/mol), the existence of oligomeric forms of the precursor, and the presence of phosphate in the precursor (15-20 mol/mol of protein). Phosphoserine was identified in the precursor, but neither phosphothreonine nor phosphotyrosine was observed. The results of proteolytic digests of [32P]phosphate-radiolabeled precursor show that the phosphate is unevenly distributed throughout the molecule and may be localized in approximately 30% of the precursor. A discrete localization of the phosphate in the precursor may block a specific keratin filament combining site and so prevent premature aggregation of these filaments during epidermal differentiation. It is suggested that a specific phosphatase is involved in the dephosphorylation, because several phosphatases of general specificity, including rat epidermal lysosomal acid phosphatase, did not catalyze this conversion.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins / Q000032:analysis / Q000378:metabolism*; D007633:Keratins / Q000378:metabolism; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D011498:Protein Precursors / Q000032:analysis / Q000378:metabolism*; D051381:Rats
D000596:Amino Acids; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D010446:Peptide Fragments; D010710:Phosphates; D011498:Protein Precursors; D007633:Keratins; D010744:Phosphoric Monoester Hydrolases