The oligosaccharide moieties of the epidermal growth factor receptor in A-431 cells. Presence of complex-type N-linked chains that contain terminal N-acetylgalactosamine residues.

The receptor for epidermal growth factor (EGF) in the human epidermoid carcinoma cell line A-431 is a glycoprotein of apparent molecular weight = 170,000.During biosynthesis, the receptor is first detected as a precursor of apparent Mr = 160,000.In this report we describe our studies on the structures of the oligosaccharide moieties of the mature receptor and its precursor.A-431 cells were grown in medium containing radioactive sugars and the radiolabeled receptors were purified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis.Radiolabeled glycopeptides were prepared from the purified receptor by proteolysis, and their structures were examined by a variety of techniques.The mature EGF receptor contains both complextype and high mannose-type Asn-linked oligosaccharides in the approximate ratio of 2 to 1, while the precursor contains only high mannose-type chains.A number of experimental results demonstrate that the mature receptor does not contain oligosaccharides in O-linkage through N-acetylgalactosamine to either serine or threonine.The high mannose-type oligosaccharides in both precursor and mature receptor can be cleaved by endo-B-N-acetylglucosaminidase H and occur in the mature receptor as Man9GlcNAc2 (6%), MansGlcNAc2 (49%), Man7GlcNAc2 (25%), and Man6-GlcNAc2 (20%), whereas, in the receptor precursor the high mannose chains occur primarily as Mans-The complex-type oligosaccharides in the mature re- ceptor are predominantly trior tetraantennary species and are unusual in several respects.(i) Many of the chains do not contain sialic acid, while the remaining chains contain 1-2 sialic acid residues.(ii) Half of the [3H]mannose-derived radioactivity was recovered as [3H]fucose and the remaining half as r3H]mannose, indicating that there may be an average of 3 fucose residuesjchain.(iii) About one-third of the [3H]glucosamine-derived radioactivity in these glycopeptides was recovered as N-acetylgalactosamine and these residues are all a-linked and occur at the nonreducing termini.