Heterogeneous glycosylation of murine transferrin receptor subunits

Abstract

The N-linked glycosylation of the murine receptor for transferrin has been investigated. Previously we have found that purified receptors appear as two bands after sodium dodecyl sulfate/polyacrylamide gel electrophoresis and Coomassie blue staining [van Driel, I. R., Stearne, P. A., Grego, B., Simpson, R. J. and Goding, J. W. (1984) J. Immunol. 133,3220 -32241. In the current report we show that the two bands are due to different glycosylation of individual receptor molecules. The receptors have three asparagines to which N-linked glycans can be added, but only two sites are glycosylated in all receptors. The level of glycosylation of the third site varies depending on cell line or tissue. Limited endoglycosidase digestion of mature receptors indicates that differential glycosylation probably occurs at only one particular asparagine residue. Possible mechanisms that could result in such a glycosylation pattern are discussed.The cell surface receptor for transferrin in mouse and man is a disulfide-linked dimeric glycoprotein with approximate monomeric M , of 90000-95000 [l-71. The structure and biosynthesis of the human receptor have previously been investigated [2,6]. These studies showed that the mature human receptors have three N-linked glycans, two of which are of the high-mannose type and the other is of the complex type [2, 71. All human receptor monomers appear to have the same number and classes of N-linked glycans and in all other respects examined seem identical. Thus, the human receptor is probably a homodimer.Recently we have purified murine transferrin receptors to apparent homogeneity by a one-step procedure based on its physiology [8]. We found that, in contrast to the human transferrin receptor, the murine receptor appeared as two closely spaced bands on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). In this report we have determined that the two species correspond to receptor molecules that have different numbers of N-linked oligosaccharides. We have investigated this differential glycosylation using a combination of two-dimensional gel electrophoresis and digestion with glycosidases. MATERIALS AND METHODS Cell lines and miceCells were maintained in exponential growth in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum.

Murine plasma cell membrane antigen PC-1: molecular cloning of cDNA and analysis of expression.

“…Our finding that a rat gene hybridizes to a murine PC-1 cDNA strengthens the argument that rats possess a homologue of PC-1. A similar protein is also present on antibody-secreting cells in the hamster (4). As yet there is no evidence for a human PC-1 homologue.…”

“…The plasma cell antigen PC-1 is the only murine lymphocyte protein known to be expressed exclusively on the surface of terminally differentiated B lymphocytes (1,2), but as yet its function is unknown. We are currently investigating the structure of PC-1 (2)(3)(4) in an attempt to gain some indication of its role in the final stage of B-cell maturation. At present, it is plausible that PC-1 is involved in the secretory mechanism (2), is a receptor for a lymphokine needed for B-cell growth or differentiation, or has some other recognition function.…”

“…Biochemical analysis has demonstrated that PC-1 is an acidic disulfide-bonded dimeric membrane protein with indistinguishable subunits of relative molecular mass (Mr) 120,000 (2)(3)(4)21). Thus PC-1 is one of only three known disulfide-bonded homodimeric proteins, the others being the transferrin receptor (22)(23)(24) and the T8 antigen (17).…”

“…Thus PC-1 is one of only three known disulfide-bonded homodimeric proteins, the others being the transferrin receptor (22)(23)(24) and the T8 antigen (17). PC-1 homologues have been identified in the rat and hamster (4). Indirect evidence for PC-1 being found in the brain, liver, and kidney has been reported (1,4,25).…”

“…PC-1 homologues have been identified in the rat and hamster (4). Indirect evidence for PC-1 being found in the brain, liver, and kidney has been reported (1,4,25).…”