| First Author | Shen F | Year | 1997 |
| Journal | Biochem J | Volume | 327 ( Pt 3) |
| Pages | 759-64 | PubMed ID | 9581553 |
| Mgi Jnum | J:44248 | Mgi Id | MGI:1099622 |
| Doi | 10.1042/bj3270759 | Citation | Shen F, et al. (1997) Expression levels of functional folate receptors alpha and beta are related to the number of N-glycosylated sites. Biochem J 327(Pt 3):759-64 |
| abstractText | In a previous study with inhibitors of N-glycosylation, it was proposed that core glycosylation of the folate receptor (FR) is required for the proper folding of the protein [Luhrs (1991) Blood 77, 1171-1180]. The human FR isoforms type alpha and type beta have three and two candidate sites for N-glycosylation respectively, only one of which is conserved. The significance of N-glycosylation at each of these loci in the expression and function of FR was examined by eliminating the sites both individually and in combination by introducing Asn-->Gln substitutions. Translation experiments in vitro showed that the mutations did not alter the synthetic rates of the polypeptides. The recombinant proteins were expressed in human 293 fibroblasts. Treatment with N-glycanase and analysis by Western blotting of the wild-type and mutant proteins revealed that all of the candidate sites in both FR-alpha and FR-beta are glycosylated. When all of the N-glycosylation sites were abolished, 2% and 8% of FR-alpha and FR-beta respectively were expressed on the cell surface compared with the corresponding wild-type proteins; the residual FR polypeptides in the cell lysates were unable to bind [3H]folic acid. In both the proteins, the inclusion of each additional N-glycosylation site partly contributed to restoration of cell surface [3H]folic acid binding and receptor-mediated folate transport. Further, in FR-beta the introduction of an additional unnatural site of N-glycosylation resulted in the enhancement of the expression of the cell surface receptor compared with the wild-type protein. The results indicate that the total mass of N-glycosylation, not a specific locus of the modification, is critical for the efficient folding and optimal expression of functional FR-alpha and FR-beta. |
