Description |
Low Density Lipoprotein Receptor-Related Protein Associated Protein 1 (LRPAP1), also known as Receptor-Associated Protein (RAP), is a novel type of chaperone that assists in the biosynthesis and intracellular transport of endocytic receptors. Experimental evidence suggests that LRPAP1/RAP acts as a receptor antagonist and prevents association of newly synthesized receptors with their ligands during transport to the cell surface. This mechanism seems to be required in cell types that express both receptor and ligand because premature receptor-ligand interaction in the secretory pathway interferes with proper export of the receptors to the cell surface. LRPAP1/RAP is a 39 kDa receptor-associated protein capable of universally inhibiting ligand interaction with members of the LDL Receptor family that mediate endocytosis and signal transduction of many extracellular ligands which participate in lipoprotein metabolism, protease regulation, embryonic development, and the pathogenesis of disease. It also binds tightly to gp330, an endocytic receptor that resembles LRP and is abundantly expressed in the kidney, and to the Very Low Density Lipoprotein (VLDL) Receptor. LRPAP1/RAP promotes the proper folding of these receptors, a function that is likely independent from its ability to inhibit ligand binding. Some evidence suggests LRPAP1/RAP may play a role in regulating the expression of LRP, possibly by stabilizing the receptor during biosynthesis or transport along the secretory pathway, and could be a short-acting modulator of LRP activity. |