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J Mol Biol. 2018 Oct 19;430(21):4102-4118. doi: 10.1016/j.jmb.2018.08.009. Epub 2018 Aug 16.

A Novel Polar Core and Weakly Fixed C-Tail in Squid Arrestin Provide New Insight into Interaction with Rhodopsin.

Author information

1
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
2
Department of Chemical and Physical Sciences, University of Toronto, Mississauga, Ontario L5L 1C6, Canada.
3
Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, USA.
4
Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
5
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada. Electronic address: oliver.ernst@utoronto.ca.

Abstract

Photoreceptors of the squid Loligo pealei contain a G-protein-coupled receptor (GPCR) signaling system that activates phospholipase C in response to light. Analogous to the mammalian visual system, signaling of the photoactivated GPCR rhodopsin is terminated by binding of squid arrestin (sArr). sArr forms a light-dependent, high-affinity complex with squid rhodopsin, which does not require prior receptor phosphorylation for interaction. This is at odds with classical mammalian GPCR desensitization where an agonist-bound phosphorylated receptor is needed to break stabilizing constraints within arrestins, the so-called "three-element interaction" and "polar core" network, before a stable receptor-arrestin complex can be established. Biophysical and mass spectrometric analysis of the squid rhodopsin-arrestin complex indicates that in contrast to mammalian arrestins, the sArr C-tail is not involved in a stable three-element interaction. We determined the crystal structure of C-terminally truncated sArr that adopts a basal conformation common to arrestins and is stabilized by a series of weak but novel polar core interactions. Unlike mammalian arrestin-1, deletion of the sArr C-tail does not influence kinetic properties of complex formation of sArr with the receptor. Hydrogen-deuterium exchange studies revealed the footprint of the light-activated rhodopsin on sArr. Furthermore, double electron-electron resonance spectroscopy experiments provide evidence that receptor-bound sArr adopts a conformation different from the one known for arrestin-1 and molecular dynamics simulations reveal the residues that account for the weak three-element interaction. Insights gleaned from studying this system add to our general understanding of GPCR-arrestin interaction.

KEYWORDS:

X-ray structure; hydrogen–deuterium exchange; phosphorylation-independent GPCR–arrestin interaction; time-resolved EPR

PMID:
30120952
DOI:
10.1016/j.jmb.2018.08.009
[Indexed for MEDLINE]

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