LC-MS/MS analysis of the cation-independent mannose 6-phosphate receptor (CI-MPR) from bovine serum

The cation-independent mannose 6-phosphate receptor (CI-MPR) is clinically significant in the treatment of patients with lysosomal storage diseases because it functions in the biogenesis of lysosomes by transporting mannose 6-phosphate (M6P)-containing lysosomal enzymes to endosomal compartments. The extracellular region of CI-MPR comprises 15 homologous domains with binding sites for M6P-containing ligands located in domains 3, 5, 9, and 15, whereas IGF2 interacts with residues in domain 11. To evaluate the allosteric properties and conformation of CI-MPR, we isolated the receptor from a mammalian source, bovine serum and analyzed the sequence of the isolated receptor by mass spectrometry.