The Role of ICL1 and H8 in Class B1 GPCRs; Implications for Receptor Activation

Abstract

The first intracellular loop (ICL1) of G protein-coupled receptors (GPCRs) has received little attention, although there is evidence that, with the 8th helix (H8), it is involved in early conformational changes following receptor activation as well as contacting the G protein β subunit. In class B1 GPCRs, the distal part of ICL1 contains a conserved R12.48KLRCxR2.46b motif that extends into the base of the second transmembrane helix; this is weakly conserved as a [R/H]12.48KL[R/H] motif in class A GPCRs. In the current study, the role of ICL1 and H8 in signaling through cAMP, iCa2+ and ERK1/2 has been examined in two class B1 GPCRs, using mutagenesis and molecular dynamics. Mutations throughout ICL1 can either enhance or disrupt cAMP production by CGRP at the CGRP receptor. Alanine mutagenesis identified subtle differences with regard elevation of iCa2+, with the distal end of the loop being particularly sensitive. ERK1/2 activation displayed little sensitivity to ICL1 mutation. A broadly similar pattern was observed with the glucagon receptor, although there were differences in significance of individual residues. Extending the study revealed that at the CRF1 receptor, an insertion in ICL1 switched signaling bias between iCa2+ and cAMP. Molecular dynamics suggested that changes in ICL1 altered the conformation of ICL2 and the H8/TM7 junction (ICL4). For H8, alanine mutagenesis showed the importance of E3908.49b for all three signal transduction pathways, for the CGRP receptor, but mutations of other residues largely just altered ERK1/2 activation. Thus, ICL1 may modulate GPCR bias via interactions with ICL2, ICL4 and the Gβ subunit.

Publication DOI: https://doi.org/10.3389/fendo.2021.792912
Divisions: College of Health & Life Sciences > School of Biosciences
College of Health & Life Sciences
College of Health & Life Sciences > Aston Pharmacy School
Aston University (General)
Additional Information: © 2022 Winfield, Barkan, Routledge, Robertson, Harris, Jazayeri, Simms, Reynolds, Poyner and Ladds. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Funding: This work was supported by the following BBSRC grants (BB/M00015X/1 (to GL), BB/M000176/1 (to DRP), and BB/M006883/1 (to C.A.R.), MRC Doctoral Training Partnership MR/J003964/1 (to IW), the BBSRC-funded Midlands Integrative Biosciences Training Partnership (MIBTP) (KB).
Uncontrolled Keywords: Endocrinology,GPCRs,signaling bias,CLR,RAMPs,mutagenesis
Publication ISSN: 1664-2392
Last Modified: 26 Nov 2024 08:12
Date Deposited: 31 Jan 2022 09:48
Full Text Link:
Related URLs: https://www.fro ... 021.792912/full (Publisher URL)
PURE Output Type: Article
Published Date: 2022-01-13
Accepted Date: 2021-12-15
Submitted Date: 2021-10-11
Authors: Winfield, Ian
Barkan, Kerry
Routledge, Sarah
Robertson, Nathan J.
Harris, Matthew
Jazayeri, Ali
Simms, John (ORCID Profile 0000-0002-4675-0902)
Reynolds, Christopher A.
Poyner, David R. (ORCID Profile 0000-0003-1590-112X)
Ladds, Graham

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