Molecular determinants on extracellular loop domains that dictate interaction between β‐arrestin and human APJ receptor

The human APJ receptor (APJR), activated by apelin isoforms, regulates cardiovascular functions and fluid homeostasis. Understanding its structure‐function relationship is crucial for a comprehensive knowledge of signalling aberrations that cause several physiological disorders. Here, we demonstrate the influence of extracellular loop (ECL) domains in the mechanism of β‐arrestin‐mediated signalling from human APJR: Apelin system. Alanine mutations of evolutionarily conserved residues were characterized using receptor internalization, β‐arrestin pull‐down, Akt phosphorylation and cell migration assay. C281A and 268 KTL 270 ‐AAA in ECL3 were deficient in all assays, whereas 183 MDYS 186 ‐AAAA mutant in ECL2 showed impaired β‐arrestin‐mediated signalling but demonstrated G i ‐dependent cell migration. Our findings establish that conserved residues in the extracellular domain play a prominent role in modulating receptor interactions with the β‐arrestin signalling cascade.