Abstract
The transferrin receptor undergoes extensive co- and post-translational modifications during its biosynthesis. In this study, the functional and structural properties of the transferrin receptor from tunicamycin-treated A431 cells were examined. Incubation of A431 cells with this inhibitor of asparagine-linked glycosylation results in a shift of the apparent molecular weight of the transferrin receptor from 94,000 to 79,000. The electrophoretic mobility of the receptor from treated cells is that of a monomer under nonreducing conditions, whereas the transferrin receptor in untreated cells has the mobility of a dimer under identical conditions. This result indicates a lack of disulfide bond formation between subunits of the receptor from tunicamycin-treated cells. In solution no dimers can be detected with cross-linking studies. This unglycosylated receptor does not appear to stably bind transferrin as demonstrated by a lack of isolation of this form of the receptor with transferrin-linked Sepharose. It is not transported to the surface of A431 cells.
Highlights
Thetransferrinreceptorundergoes extensive co- receptor cannot be isolated on transferrin-linked Sepharose and post-translational modifications duritnsgbiosyn- under standard conditions
There is no in- cells wasable to bind transferrin (Fig. 2, lune 5).There were corporation of [3H]glucosamineinto this receptor, and the no detectable differences in untreated cellsbetween the receptor from tunicamycin-treated cells is resistant to diges- amount of transferrin receptor that could beimmunoprecipition by endoglycosidase H
The molecular tated and the amountof transferrin receptor able to bind to weight of the receptor immunoprecipitated from tunicamycin- the transferrin-linked Sepharose (Fig. 2, lunes 4 versus 5)
Summary
Thetransferrinreceptorundergoes extensive co- receptor cannot be isolated on transferrin-linked Sepharose and post-translational modifications duritnsgbiosyn- under standard conditions. The properties of the unglycosylated transferrin receptor in tunicamycin-treated cells were examined. Our experiments demonstratethat thuenglycosylated transferrin receptor from tunicamycin-treated cells lacks intersubunit disulfide bonds, forms no detectable dimer in solution, and is not transported to thecell surface.
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