Date Published: March 15, 2019
Publisher: Public Library of Science
Author(s): Chen Zheng, Jonas Tholen, Vsevolod V. Gurevich, Arun Shukla.
We tested the interactions with four different G protein-coupled receptors (GPCRs) of arrestin-3 mutants with substitutions in the four loops, three of which contact the receptor in the structure of the arrestin-1-rhodopsin complex. Point mutations in the loop at the distal tip of the N-domain (Glu157Ala), in the C-loop (Phe255Ala), back loop (Lys313Ala), and one of the mutations in the finger loop (Gly65Pro) had mild variable effects on receptor binding. In contrast, the deletion of Gly65 at the beginning of the finger loop reduced the binding to all GPCRs tested, with the binding to dopamine D2 receptor being affected most dramatically. Thus, the presence of a glycine at the beginning of the finger loop appears to be critical for the arrestin-receptor interaction.
G-protein coupled receptors (GPCRs) are the largest family of signaling proteins in mammals, with ~500 different subtypes in dolphins, ~800 in primates, and more than 3,400 in elephants (sevens.cbrc.jp). GPCRs are involved in almost every aspect of life activity by mediating most cellular responses to hormones, neurotransmitters, odorants, light, etc. .
Mutations in numerous proteins underlie a variety of human disorders. Mutations in GPCRs fall into two categories: loss- and gain-of-function [11,12]. Despite the initial enthusiasm about editing errors out of the genome, careful studies show that CRISPR/Cas-9 gene editing often generates off-target changes, some of which could be expected, whereas others could not . In more traditional gene therapy approach, the strategy in case of loss-of-function mutations is clear: the delivery of the coding sequence for the normal receptor should solve the problem. Loss-of-function mutations are usually recessive, as one normal allele is in most cases sufficient, so that only compound heterozygotes are affected. In contrast, gain-of-function mutations are dominant: normal product of the second allele cannot dampen the signaling by an overactive mutant receptor. One strategy was proposed to fight gain-of-function GPCR mutations: dampening their excessive signaling with enhanced arrestins that have higher propensity to bind these receptors. So far this compensational approach had shown promise in the visual system, where the only important receptor is rhodopsin, which is shut off by arrestin-1 [13,46]. While due to highly conserved activation mechanisms non-visual arresins can be enhanced by the same mutations as visual arrestin-1 [47–49], non-visual arrestins have broad receptor specificity [15,50,51]. Most cells express multiple GPCR subtypes. While the expression of enhanced non-visual arrestin would likely dampen excessive signaling by the mutant, at the same time it would reduce the signaling of perfectly normal other GPCRs in the same cell. Thus, the use of the same compensational approach requires non-visual arrestin variants with narrow receptor specificity, that would target only the “offending” receptor mutant, but not the other GPCRs.