Description
RAP binds with high affinity to certain members of the low-density lipoprotein (LDL) receptor family such as LDL receptor-related protein (LRP), gp330/megalin, and the very low-density lipoprotein (VLDL) receptor and, once bound to these receptors, antagonizes their ligand binding ability. Despite the presence of a putative signal sequence on RAP, this molecule is not secreted but remains cell-associated. RAP is contained primarily within the endoplasmic reticulum and Golgi compartments, with only a trace found at the cell surface and within the endosomal compartments. Genetic deletion of RAP in mice has no effect on LRP mRNA levels but does lead to incomplete processing of LRP in the brain and liver resulting in decreased LRP antigen levels in these organs