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 beta-arrestin-mediated signalling from human APJR: Apelin system. Alanine mutations of evolutionarily conserved residues were characterized using receptor internalization, beta-arrestin pull-down, Akt phosphorylation and cell migration assay. C281A and (KTL270)-K-268-AAA in ECL3 were deficient in all assays, whereas (MDYS186)-M-183-AAAA mutant in ECL2 showed impaired beta-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 beta-arrestin signalling cascade.