A protease-resistant, transformation-sensitive membrane glycoprotein and an intermediate filament-forming protein of hamster embryo fibroblasts.

A transformation-sensitive membrane glycoprotein with a subunit molecular weight of 170,000 (170K), a M, = 56,000 protein identified as an “intermediate filament forming protein” (IFP) of hamster embryo fibroblasts, and possible interaction of these two components are described. The 170K glycoprotein has been characterized as follows: 1) weak surface labeling by either lactoperoxidase-catalyzed iodination, or galactose oxidase oxidation and reduction with tritiated sodium borohydride; 2) strong metabolic labeling with [“Hlglucosamine; 3) resistance to trypsin digestion, under which condition “galactoprotein a” (Gap a or LETS) was degraded completely; 4) deletion in clones of polyoma-transformed NIL cells (NILpy); and 5) possession of a disulfide-dependent subunit interaction. The intermediate filament protein, subunit molecular weight of 56,000, had an electrophoretic mobility distinct from either actin or tubulin and could be polymerized in the presence of millimolar quantities of guanosine triphosphate, magnesium, and calcium ions at 25°C to form filaments of 105 b diameter. The polymerization of IFP was increased by calcium ion and inhibited by addition of reduced glutathione or dithiothreitol to the sucrose/ATP extraction buffer. A possible association of the 170K glycoprotein with IFP has been suggested by: 1) IFP can be co-purified with 170K glycoprotein from the cold sucrose/ATP extract of cells through a Ricinus communis lectin-polyacrylhydrazidoSepharose column although IFP has no receptor for Ricinus communis lectin; and 2) IFP and 170K glycoprotein were coprecipitated when IFP was polymerized from sucrose/ATP extracts of cells.