LRPAP1 is involved with trafficking of certain members of the LDL receptor family including LRP1 and LRP2.The alpha-2-macroglobulin receptor complex, as purified by affinity chromatography, contains 3 polypeptides: a 515-kD heavy chain, an 85-kD light chain, and a 39-kD associated protein.The deduced amino acid sequence contains a putative signal sequence that precedes the 323-residue mature protein. The sequence showed 73% identity with a rat protein reported to be a pathogenic domain of the Heymann nephritis antigen gp330 and 77% identity to a 44-kD mouse heparin-binding protein termed HBP-44. There are also similarities between MRAP and apolipoprotein E. Studies indicated that the molecule is present on the cell surface, forming a complex with the heavy and light chains of the alpha-2-macroglobulin receptor.