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. 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. while divalent cations are not essential for ligand binding by the human cd-mpr, the nomenclature has been retained.