Low density lipoprotein receptor-related protein associated protein 1 also known as LRPAP1 or RAP is a chaperone protein which in humans is encoded by the LRPAP1 gene. LRPAP1 is involved with trafficking of certain members of the LDL receptor family including LRP1 and LRP2. It is a glycoprotein that binds to the alpha-2-macroglobulin receptor, as well as to other members of the low density lipoprotein receptor family. It acts to inhibit the binding of all know ligands for these receptors, and may prevent receptor aggregation and degradation in the endoplasmic reticulum, thereby acting as a molecular chaperone. It may be under the regulatory control of calmodulin, since it is able to bind calmodulin and be phosphorylated by calmodulin-dependent kinase II.