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 (PubMed:1712782, PubMed:1400426, PubMed:7774585, PubMed:16938309, PubMed:16678114, PubMed:32296178). Interacts with LRP2/glycoprotein 330 (PubMed:1400426). Interacts with LRP1B; binding is followed by internalization and degradation (PubMed:11384978). Interacts with LDLR (PubMed:16630895). Interacts with SORL1 (PubMed:8940146, PubMed:11294867, PubMed:12530537, PubMed:15053742, PubMed:15364913, PubMed:26858303). Interacts with LRP1; this interaction is followed by rapid internalization (PubMed:15053742). May be associated with receptors at the cell surface. N-glycosylated. The disease is caused by variants affecting the gene represented in this entry. Belongs to the alpha-2-MRAP family.