TY - JOUR
T1 - An insulin-like growth factor II (IGF-II) affinity-enhancing domain localized within extracytoplasmic repeat 13 of the IGF-II/Mannose 6-phosphate receptor
AU - Devi, Gayathri R.
AU - Byrd, James C.
AU - Slentz, Dorothy H.
AU - MacDonald, Richard G.
PY - 1998
Y1 - 1998
N2 - Insulin-like growth factor II (IGF-II) and phosphomannosylated glycoproteins bind to distinct sites on the same receptor, the IGF- II/mannose 6-phosphate receptor (IGF2R). Analysis of truncated receptors (minireceptors) has been used to map the IGF-II binding site within the receptor's extracytoplasmic domain, which consists of 15 homologous repeats. A minireceptor consisting of repeat 11 contained the minimal elements for binding IGF-II, but with 5- to 10-fold lower relative binding affinity than the full-length receptor. We hypothesized that the complete, high-affinity IGF-II binding site is formed by interaction between the primary site in repeat 11 and a putative affinity-enhancing domain. To determine the minimum portion of the IGF2R's extracytoplasmic domain needed for expression of high- affinity IGF-II binding, a nested set of FLAG epitope-tagged minireceptors encompassing repeats 11 through 15 was prepared and transiently expressed in 293T cells. Minireceptors containing repeats 11-13 or 11-15 exhibited high affinity, comparable to the full-length receptor (IC50 = 1-2 nM), whereas constructs containing repeat 11 only or repeats 11-12 did not (IC50 = 10- 20 nM). These data suggested that the affinity-enhancing domain is located within repeat 13, which contains a unique 43-residue insert that has ~50% sequence identity to the type II repeat of fibronectin. Although a repeat 13 minireceptor did not bind IGF-II on its own, an 11-13 minireceptor containing a deletion of the 43-residue insert exhibited low IGF-II binding affinity (IC50 = 10-20 nM). Expression of mutant receptors from a full-length IGF2R construct bearing a deletion of the 43-residue insert was very low relative to wild type. Depletion assays using IGF-II-Sepharose showed that the mutant receptor had lower affinity for IGF-II than the wild-type receptor. This study reveals that two independent receptor domains are involved in the formation of a high-affinity binding site for IGF-II, and that a complete repeat 13 is required for high-affinity IGF-II binding.
AB - Insulin-like growth factor II (IGF-II) and phosphomannosylated glycoproteins bind to distinct sites on the same receptor, the IGF- II/mannose 6-phosphate receptor (IGF2R). Analysis of truncated receptors (minireceptors) has been used to map the IGF-II binding site within the receptor's extracytoplasmic domain, which consists of 15 homologous repeats. A minireceptor consisting of repeat 11 contained the minimal elements for binding IGF-II, but with 5- to 10-fold lower relative binding affinity than the full-length receptor. We hypothesized that the complete, high-affinity IGF-II binding site is formed by interaction between the primary site in repeat 11 and a putative affinity-enhancing domain. To determine the minimum portion of the IGF2R's extracytoplasmic domain needed for expression of high- affinity IGF-II binding, a nested set of FLAG epitope-tagged minireceptors encompassing repeats 11 through 15 was prepared and transiently expressed in 293T cells. Minireceptors containing repeats 11-13 or 11-15 exhibited high affinity, comparable to the full-length receptor (IC50 = 1-2 nM), whereas constructs containing repeat 11 only or repeats 11-12 did not (IC50 = 10- 20 nM). These data suggested that the affinity-enhancing domain is located within repeat 13, which contains a unique 43-residue insert that has ~50% sequence identity to the type II repeat of fibronectin. Although a repeat 13 minireceptor did not bind IGF-II on its own, an 11-13 minireceptor containing a deletion of the 43-residue insert exhibited low IGF-II binding affinity (IC50 = 10-20 nM). Expression of mutant receptors from a full-length IGF2R construct bearing a deletion of the 43-residue insert was very low relative to wild type. Depletion assays using IGF-II-Sepharose showed that the mutant receptor had lower affinity for IGF-II than the wild-type receptor. This study reveals that two independent receptor domains are involved in the formation of a high-affinity binding site for IGF-II, and that a complete repeat 13 is required for high-affinity IGF-II binding.
UR - http://www.scopus.com/inward/record.url?scp=0031724560&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0031724560&partnerID=8YFLogxK
U2 - 10.1210/mend.12.11.0192
DO - 10.1210/mend.12.11.0192
M3 - Article
C2 - 9817593
AN - SCOPUS:0031724560
SN - 0888-8809
VL - 12
SP - 1661
EP - 1672
JO - Molecular Endocrinology
JF - Molecular Endocrinology
IS - 11
ER -