Characterization of mannose 6-phosphate receptors (MPRs) from opossum liver: opossum cation-independent MPR binds insulin-like growth factor-II.
Bovine, human, and rat cation-independent mannose 6-phosphate receptors (CI-MPRs) are capable of binding both mannose 6-phosphate and insulin-like growth factor-II (IGF-II). However, the receptor isolated from either chicken or frog lacks the high affinity IGF-II-binding site. To determine whether CI-MPRs isolated from a species that is closely related to placental mammals can bind IGF-II, the MPRs were purified from a marsupial, the American opossum (Didelphis virginiana), by phosphomannan-Sepharose affinity chromatography and then tested for their ability to bind IGF-II. Opossum liver expressed both the CI-MPR and the cation-dependent MPR (CD-MPR). Both receptors contained Asn-linked oligosaccharides. In contrast to CD-MPRs isolated from other species, the opossum CD-MPR displayed heterogeneity with respect to the number of Asn-linked oligosaccharide chains it contains. The CI-MPR isolated from opossum liver, like the CI-MPR from bovine liver, bound iodinated human recombinant IGF-II. However, Scatchard analysis revealed that the opossum CI-MPR bound IGF-II with a lower affinity (Kd = 14.5 nM) than the bovine receptor (Kd = 0.2 nM). The addition of excess IGF-II, but not IGF-I or insulin, inhibited binding to [125I]IGF-II, indicating that the opossum CI-MPR exhibits specificity for IGF-II. These results suggest that the emergence of a high affinity IGF-II-binding site in the CI-MPR occurred in evolution before the divergence of marsupials and placental mammals from their last common ancestor.
Dahms
N M
NM
Department of Biochemistry, Medical College of Wisconsin, Milwaukee 53226.
Brzycki-Wessell
M A
MA
Ramanujam
K S
KS
Seetharam
B
B
D000818:Animals; D001216:Asparagine / Q000032:analysis; D001665:Binding Sites; D002412:Cations; D002417:Cattle; D002846:Chromatography, Affinity; D006801:Humans; D007163:Immunosorbent Techniques; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008099:Liver / Q000737:chemistry*; D009844:Oligosaccharides / Q000032:analysis; D009893:Opossums; D017527:Receptor, IGF Type 2 / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D002412:Cations; D007457:Iodine Radioisotopes; D009844:Oligosaccharides; D017527:Receptor, IGF Type 2; D011994:Recombinant Proteins; D007335:Insulin-Like Growth Factor II; D001216:Asparagine