Molecular chaperone for LDL receptor-related proteins that may regulate their ligand binding activity along the secretory pathway. Interacts with the LRP1/alpha-2-macroglobulin receptor heavy and light chains; the interaction is transient and coincides with a reduction of ligand binding by the receptor. Interacts with LRP2/glycoprotein 330. Interacts with LRP1B; binding is followed by internalization and degradation. Interacts with LDLR. Interacts with SORL1 (By similarity). Interacts with LRP1; this interaction is followed by rapid internalization (By similarity). May be associated with receptors at the cell surface. Highly expressed in PYS-2 parietal endoderm cells and in the kidney. The RNA level increased about 10-fold during differentiation of F9 embryonal carcinoma cells to parietal endoderm cells. N-glycosylated. Belongs to the alpha-2-MRAP family.