Isolation and characterization of keratin-like proteins from cultured cells with fibroblastic morphology.
Intermediate filaments (IF) isolated from a variety of cultured cells, conventionally described as fibroblasts, are composed predominantely of proteins of molecular weights of 54,000 and/or 55,000. Less than 15% of the protein found in native IF preparations from these cells is composed of three to four polypeptides of molecular weights 60,000-70,000. We have investigated some biochemical and immunological properties of these proteins isolated from BHK-21 and mouse 3T3 cells. They are capable of forming paracrystals that exhibit a light/dark banding pattern when negatively stained with uranyl acetate. The dark bands are composed of longitudinally aligned approximately 2-nm-diam filaments. The center-to-center spacing between either dark or light bands is 37-40 nm. These dimensions are consistent with the secondary structure of IF polypeptides and suggest that the dark bands represent lateral alignment of alpha-helical coiled-coil domains. Immunoblotting, secondary structure, as well as amino acid composition data indicate that the 60,000-70,000-mol-wt paracrystal polypeptides are similar to keratin. Thus, polypeptides with biochemical and immunological properties of epidermal keratin are present in cells normally considered to be fibroblasts.
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000648:ultrastructure*; D004591:Electrophoresis, Polyacrylamide Gel; D007381:Intermediate Filament Proteins / Q000302:isolation & purification*; D007633:Keratins; D007668:Kidney; D008854:Microscopy, Electron; D008970:Molecular Weight; D011506:Proteins / Q000302:isolation & purification*
D007381:Intermediate Filament Proteins; D011506:Proteins; D007633:Keratins