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. 2021 Aug 20;12:5064. doi: 10.1038/s41467-021-25364-2

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — a, b Structural superposition of the active and antagonist-bound ghrelin receptor. (a) side view; (b) cytoplasmic view. c, d Conformational changes of the salt bridge comprising of E124^3.33 and R283^6.55 upon peptide activation. Ghrelin and GHRP-6 push the side-chain of R283^6.55 to swing away from the receptor helical core due to steric clash. The swing orientations of E124^3.33 and R283^6.55 were indicated by red arrows. The clashes were highlighted as red oval dashed lines. e-h Conformational changes of the conserved “micro-switches” upon receptor activation. (e) Toggle switch, (f) ERY motif, (g) PIF motif, (h) NPxxY motif. The outward displacement of TM6 of the active receptor is shown as a red arrow (e). The conformational changes of residue side chains are shown as red arrows upon receptor activation. i The hydrophobic cluster comprising F279^6.51, F309^7.39, F312^7.42, and Y313^7.43 stabilizes the inter-helical hydrophobic contacts between TM6 and TM7. Ghrelin is shown in magenta, ghrelin-bound ghrelin receptor in slate blue. GHRP-6 is displayed in green, and GHRP-6 bound ghrelin receptor in salmon. The compound 21-bound ghrelin receptor (PDB: 6KO5), is colored in gray.