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Chicken and Xenopus mannose 6-phosphate receptors fail to bind insulin-like growth factor II
1Department of Biochemistry, University of Massachusetts Medical Center, Worcester 01655.
Abstract:
The recent demonstration that a single mammalian receptor protein binds both mannose 6-phosphate (Man-6-P) and insulin-like growth factor II (IGF-II) with high affinity has suggested a multifunctional physiological role for this receptor, possibly including signal transduction. In order to better understand the functions of this receptor, we have investigated the properties of Man-6-P receptors from non-mammalian species. Receptors were affinity-purified from Triton X-100 extracts of total membranes from Xenopus and chicken liver as well as rat placenta using pentamannosyl 6-phosphate-Sepharose. The Man-6-P receptor was adsorbed to the pentamannosyl 6-phosphate-Sepharose and specifically eluted by Man-6-P in all three species, as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining. When the purified receptors from these three species were cross-linked to 125I-IGF-II with disuccinimidyl suberate, only receptors isolated from rat membranes were affinity-labeled. To further evaluate the properties of these Man-6-P receptors, binding of 125I-rat-IGF-II and 125I-chicken Tyr-Gly-Thr-Ala-IGF-II to purified receptors from Xenopus, chicken, and rat was evaluated by polyethylene glycol precipitation. Only the rat Man-6-P receptor exhibited detectable binding of 125I-IGF-II. These data suggest that the emergence of a high affinity IGF-II binding site on the Man-6-P receptor occurred in evolution after the divergence of mammals from other vertebrates. Thus, the biological actions of IGF-II in chickens and frogs appear to be initiated by the type I IGF receptor.
Insights
The mannose 6-phosphate (Man-6-P) receptor binds insulin-like growth factor II (IGF-II) in mammals, but not in Xenopus or chickens. This suggests IGF-II binding evolved later in mammals, with other receptors mediating its actions in non-mammalian vertebrates.
Area of Science:
- Biochemistry
- Evolutionary Biology
- Cell Biology
Background:
- A single mammalian receptor protein exhibits high-affinity binding for both mannose 6-phosphate (Man-6-P) and insulin-like growth factor II (IGF-II).
- This dual binding suggests a multifunctional physiological role for the Man-6-P receptor, potentially involving signal transduction.
- Understanding the evolutionary origins of this dual function is crucial for elucidating receptor roles across species.
Purpose of the Study:
- To investigate the properties of Man-6-P receptors in non-mammalian species.
- To determine if the Man-6-P receptor in non-mammalian vertebrates also binds IGF-II.
- To understand the evolutionary timeline of IGF-II binding to the Man-6-P receptor.
Main Methods:
- Affinity purification of Man-6-P receptors from Xenopus and chicken liver, and rat placenta membranes using pentamannosyl 6-phosphate-Sepharose.
- Analysis of purified receptors using SDS-PAGE and silver staining.
- Cross-linking studies with 125I-IGF-II and polyethylene glycol precipitation assays to evaluate IGF-II binding.
Main Results:
- Man-6-P receptors were successfully purified from all three species and specifically eluted by Man-6-P.
- Only rat Man-6-P receptors showed affinity labeling when cross-linked to 125I-IGF-II.
- Detectable binding of 125I-IGF-II was observed exclusively with the purified rat Man-6-P receptor.
Conclusions:
- The high-affinity binding site for IGF-II on the Man-6-P receptor emerged in evolution after the divergence of mammals from other vertebrates.
- In non-mammalian vertebrates like chickens and frogs, the biological actions of IGF-II are likely mediated by the type I IGF receptor.
- This study highlights the evolutionary acquisition of dual ligand binding specificity in the Man-6-P receptor.