Structure of the Human Cation-Independent Mannose 6-Phosphate/IGF2 Receptor Domains 7–11 Uncovers the Mannose 6-Phosphate Binding Site of Domain 9

The cation-independent mannose 6-phosphate (M6P)/Insulin-like growth factor-2 receptor (CI-MPR/IGF2R) is an ∼300 kDa transmembrane protein responsible for trafficking M6P-tagged lysosomal hydrolases and internalizing IGF2. The extracellular region of the CI-MPR has 15 homologous domains, including M6P-binding domains (D) 3, 5, 9, and 15 and IGF2-binding domain 11. We have focused on solving the first structures of human D7–10 within two multi-domain constructs, D9–10 and D7–11, and provide the first high-resolution description of the high-affinity M6P-binding D9. Moreover, D9 stabilizes a well-defined hub formed by D7–11 whereby two penta-domains intertwine to form a dimeric helical-type coil via an N-glycan bridge on D9. Remarkably the D7–11 structure matches an IGF2-bound state of the receptor, suggesting this may be an intrinsically stable conformation at neutral pH. Interdomain clusters of histidine and proline residues may impart receptor rigidity and play a role in structural transitions at low pH. [Display omitted] •The first structure of human CI-MPR domain 9 (D9) was solved in a di-domain construct•D9–10 forms a rigid unit maintained in the crystal structure of penta-domain D7–11•D9–10 and D7–11 can dimerize through an N-linked glycan bridge on D9•The multi-domain constructs reveal two interdomain pH-sensitive interfaces Bochel et al. report the structure of the human CI-MPR/IGF2R domain 9 as part of a di-domain complex with domain 10 and a penta-domain spanning domains D7–11. D7–11 is a glycan-bridged dimer at neutral pH and reveals interdomain interfaces involved in pH-driven rearrangements.