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Receptor-associated protein (RAP) Receptor-associated protein, RAP, is an antagonist and a specialized chaperone in the endoplasmic reticulum that binds tightly to members of the low-density lipoprotein (LDL) receptor family and prevents them from associating with other ligands. RAP associates with (LDL) receptor-related protein (LRP) early in the secretory pathway, reducing its ligand binding capacity, and then dissociates from LRP in the low-pH environment of the Golgi; studies have shown that histidine residues in RAP D3 serve as a switch that facilitates its uncoupling from the receptor. RAP is a modular protein identified as having an internal triplication, with domains, D1, D2, and D3, each thought to have distinct functions; these domains are independent and do not interact. The carboxyl-terminal domain (D3) of RAP is required for folding and trafficking of LRP, while the amino-terminal tandem D1D2 domains of RAP are essential for blocking LRP from binding of certain ligands, such as activated forms of alpha2-macroglobulin. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",