Mannose 6-phosphate receptors bind newly synthesized lysosomal hydrolases in the trans-Golgi network (TGN) and deliver them to pre-lysosomal compartments. There are two different MPRs, one of ~300kDa and a smaller, dimeric receptor of ~46kDa.[2][3] The larger receptor is known as the cation-independent mannose 6-phosphate receptor (CI-MPR), while the smaller receptor (CD-MPR) requires divalent cations to efficiently recognize lysosomal hydrolases.[3] While divalent cations are not essential for ligand binding by the human CD-MPR, the nomenclature has been retained.[4]
Both of these receptors bind terminal mannose 6-phosphate with similar affinity (CI-MPR = 7 μM, CD-MPR = 8 μM)[5] and have similar signals in their cytoplasmic domains for intracellular trafficking.[6]
^Drickamer K, Taylor ME (2011). Introduction to glycobiology (3rd ed.). Oxford [u.a.]: Oxford University Press. pp. 177–181. ISBN978-0199569113.