the structure of 7 out of the 15 domains has been determined, using x-ray crystallography, and they seem to share a similar fold. the ci-mpr exists mainly as a dimer in the membrane. domains 3, 5 and 9 have been found to bind to mannose 6-phosphate. domains 3 and 9 can bind to mannose 6-phosphate with high affinity. domain 5 only binds man-6-phosphate with a weak affinity. however domain 5 has also been shown to bind to the phosphodiester, man-phosphate-glcnac. this is a safety mechanism for the cell – it means it is able to bind to lysosomal enzymes that have escaped the action of the enzyme that removes the glcnac residue. combining these 3 domains allows the ci-mpr to bind to a wide range of phosphorylated glycan structures. domain 11 binds to igf-ii.