Structural insights into endothelin receptor signalling

Figures

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  Fig. 1. ETR structures determined to date. The receptors, G proteins and agonist peptides are shown as ribbon representations. The compounds are shown as sticks.

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  Fig. 2. Binding modes of endothelin-related peptides. (A) Overall structure of ETB in complex with ET-1, viewed from within the membrane plane. ETB is depicted by ribbons, with the ECL2 β-sheet highlighted. The disulphide bonds at the N-terminus and ECL2 of ETB are shown as sticks. ET-1 is shown as a transparent surface representation and a ribbon model. The side chains of ET-1 are shown as sticks. (B) Surface representation of the ET-1-bound ETB receptor, viewed from the extracellular side. (C) Comparison of the amino acid sequences of the endothelin-related peptides. (D) The architecture of ET-1 is shown in a ribbon representation, with its side chains, N-terminal amino group (N-t) and C-terminal carboxyl group (C-t) shown as sticks. (E–G) Detailed interactions between ET-1 and ETB at the C-terminal region (E), the α-helical region (F) and the N-terminal region (G). Dashed lines indicate hydrogen bonds. (H) Superimposition of the agonist-bound ETR structures, viewed from the extracellular side. (I) Electrostatic surface presentations of the extracellular regions of ET-1-bound ETA and IRL1620-bound ETB. ET-1 in the ET-1-ETA complex structure is omitted for clarity. The electrostatic…

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  Fig. 3. Structural changes upon endothelin binding. (A) Superimposition of the ET-1-bound and ligand-free structures of the ETB receptor. The extracellular view shows the ET-1-induced movement of the TM helices that constitute the orthosteric pocket. Arrows indicate the movement of helices, with the distances of the residues at each end of the helix. (B) The ET-1-bound and apo structures are superimposed to show the structural differences propagated from the ligand-binding pocket. (C) Packing interactions that stabilize the inactive state are observed between P2855.50, V1893.40, F3326.44 and N3787.45. (D) The inward movement of TM6, including W3366.48, upon agonist binding destabilizes the packing of V1893.40, P2855.50 and F3326.44, resulting in the downward rotation of F3326.44. These changes contribute to the rotation and outward movement of the intracellular portion of TM6 and the inward movement of TM7.

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  Fig. 4. G-protein coupling of ETRs. (A and B) Structural comparison of the apo and Gi-complexed ETB receptor, viewed from the membrane plane (A) and intracellular side (B). (C) Conformational changes on the intracellular side upon Gi coupling. The residues corresponding to the D3.49R3.50Y3.51 and N7.49P7.50xxY7.53 motifs are shown as sticks. The dashed line represents a hydrogen bond. (D) Comparison of the Gα positions in the GPCR–G-protein complexes. The structures are superimposed on the receptor structure of the NTS1 C state. (E) Comparison of the Gα positions in the ETR-G-protein complexes.

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  Fig. 5. Structural basis for antagonist binding and receptor inactivation. (A) Superimposition of the ETB structures bound to ET-1, bosentan and K-8794, viewed from the extracellular side. The drugs are shown as sticks, colour-coded as in Figure 1. (B–D) Detailed interactions of bosentan (B), K-8794 (C) and IRL2500 (D) with the receptor, viewed from the extracellular side. Black dashed lines indicate hydrogen bonds. (E) The structural changes upon compound binding, focused on TM6. Black arrows indicate the inward movements of TM6, TM7 and W3366.48 upon ET-1 binding.

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  Fig. 6. Schematic representation of ETR activation. TM6, TM7 and H8 are highlighted. The residues involved in signal transduction (N1.50, D2.50, F6.44, W6.48 and N7.45) are represented with sticks. Black dashed lines indicate hydrogen bonds. Black arrows indicate the conformational changes of the receptor, and black double arrows indicate the conformational equilibrium. Black dashed double arrows mean fewer structural transitions, resulting in the basal activity or partial agonistic activity.