Structural Basis for Apelin Control of the Human Apelin Receptor

Abstract

Apelin receptor (APJR) is a key regulator of human cardiovascular function and is activated by two different endogenous peptide ligands, apelin and Elabela, each with different isoforms diversified by length and amino acid sequence. Here we report the 2.6-Å resolution crystal structure of human APJR in complex with a designed 17-amino-acid apelin mimetic peptide agonist. The structure reveals that the peptide agonist adopts a lactam constrained curved two-site ligand binding mode. Combined with mutation analysis and molecular dynamics simulations with apelin-13 binding to the wild-type APJR, this structure provides a mechanistic understanding of apelin recognition and binding specificity. Comparison of this structure with that of other peptide receptors suggests that endogenous peptide ligands with a high degree of conformational flexibility may bind and modulate the receptors via a similar two-site binding mechanism.

Apelins, ELABELA, and their derivatives: Peptidic regulators of the cardiovascular system and beyond

“…These data are congruent with the recently reported X‐ray structure of the apelin receptor, which indicates that residues Y35, W85, Y88, Y93, and Y299 are in close proximity with the aromatic C ‐terminus of apelin (Figure ) . Conversely, Pro12 substitutions did not provide the same benefits in terms of affinity/stability (i.e., compounds 14 , 15 , and 16 ; Table ) .…”

“…The first experimental X‐Ray structure of the apelin receptor in complex with AMG3054 identified two distinct ligand binding sites . The first one is deep in the pocket (site 1, Figure B), delimited by aromatic residues Tyr35 1.39 , Trp85 2.60 , Tyr88 2.63 , Tyr93 ECL1 , and Tyr299 7.43 surrounding residue (4‐Cl)Phe17 of AMG3054 (which presumably mimics residue Phe17 of apelin‐17).…”

“…The importance of Asp284 7.28 was confirmed in MD simulations of apelin‐13 with the experimental apelin receptor structure, and the role of Asp92 ECL1 and Glu174 ECL2 could be inferred from the structure. Asp92 ECL1 is located close to Lys178 ECL2 , a key element in the formation of site 2 H‐bond network, and could stabilize its conformation. Glu174 ECL2 is located close to Glu10, His11, and Lys13 in the crystal structure, Ser10, His11, and Gly13 in apelin‐17, and thus, should contribute to binding mostly through H‐bonds.…”

Mixed Fluorotryptophan Substitutions at the Same Residue Expand the Versatility of 19F Protein NMR Spectroscopy

“…Based upon Mn 2+ ‐induced PRE in AR55, the indole H ϵ 1‐N ϵ 1 of W51 is more protected from solvent than that of W24 in both DPC and SDS micelles (Figure S3). This is consistent with the topology of full‐length AR predicted on the basis of the recent crystal structure . W85 is crystallographically predicted to be fully membrane‐embedded and W95 to be membrane‐proximal in extracellular loop 1 (ECL1; Figure ).…”

“…From previous mutagenesis studies, TM1‐3 contains residues in the N‐terminal tail and ECL1 essential for apelin binding . Apelin analogue‐AR interactions in the N‐terminal tail and ECL1 were also recently crystallographically observed . To date, apela‐AR interactions remain uncharacterized.…”