Abstract
Homologous desensitization of beta2-adrenergic and other G-protein-coupled
receptors is a two-step process. After phosphorylation of agonist-occupied
receptors by G-protein-coupled receptor kinases, they bind beta-arrestins,
which triggers desensitization and internalization of the receptors.
Because it is not known which regions of the receptor are recognized
by beta-arrestins, we have investigated beta-arrestin interaction
and internalization of a set of mutants of the human beta2-adrenergic
receptor. Mutation of the four serine/threonine residues between
residues 355 and 364 led to the loss of agonist-induced receptor-beta-arrestin2
interaction as revealed by fluorescence resonance energy transfer
(FRET), translocation of beta-arrestin2 to the plasma membrane, and
receptor internalization. Mutation of all seven serine/threonine
residues distal to residue 381 did not affect agonist-induced receptor
internalization and beta-arrestin2 translocation. A beta2-adrenergic
receptor truncated distal to residue 381 interacted normally with
beta-arrestin2, whereas its ability to internalize in an agonist-dependent
manner was compromised. A similar impairment of internalization was
observed when only the last eight residues of the C terminus were
deleted. Our experiments show that the C terminus distal to residue
381 does not affect the initial interaction between receptor and
beta-arrestin, but its last eight amino acids facilitate receptor
internalization in concert with beta-arrestin2.
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