Molecular basis for the recognition of the phosphorylation pattern in the C-terminal tail of GPCRs by arrestins

Abstract

Arrestins are responsible for desensitization and internalization of activated, phosphorylated G protein-coupled receptors (GPCRs). Over the years, it became clear that they have the potential to activate certain signaling pathways which are independent from G protein signaling. The Arrestins family only comprises four members, but they interact with hundreds of GPCRs. Several studies suggested that downstream signaling by Arrestins is modulated by the phosphorylation patterns created by a small number of GPCR-specific kinases (GRKs). They are capable of introducing specific phosphorylation motifs on the cytosolic side of the receptor, which are either located at the third intracellular loop (ICL3) or at the C terminal tail. These phosphorylation motifs are ligand- and cell-dependent, which shows the highly dynamic regulatory potential of this system. Here, I used a library of synthetic phosphorylated peptides derived from the bovine Rhodopsin C-terminus to study their influence on the activation of Arrestins. I obtained a high resolution view of the conformational changes induced by different phosphorylation patterns in Arrestin-1 by NMR. In combination with other biophysical techniques, this allowed me to identify a pattern of two phosphorylations sites near the distal part of the C-terminus that are the KEY sites for the activation of Arrestins. Other motifs were found as well that may further modulate the conformational changes in Arrestins. This could explain how distinct phosphorylation patterns are capable of regulating a variety of downstream signaling events. I also showed that Arrestins differ in their potential to interact with phosphorylated C-tails which highlights the non-redundancy of β-Arrestins.