Critical APJ receptor residues in extracellular domains that influence effector selectivity
Anisha Ashokan1, Harikumar Sheela Harisankar1, Mythili Kameswaran2
1Signal Transduction Laboratory, Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, India.
The FEBS Journal
|June 2, 2021
Summary
Researchers investigated the extracellular loops of the human apelin receptor (APJR), finding specific residues crucial for ligand binding and biased signaling pathways, including G protein and β-arrestin interactions.
Area of Science:
- Molecular and Cellular Biology
- Pharmacology and Drug Discovery
- Biochemistry
Background:
- The human apelin receptor (APJR), activated by apelin peptides, is vital for numerous physiological processes.
- The precise function of extracellular loop (ECL) domain residues in APJR's ligand binding and activation remains largely uncharacterized.
Purpose of the Study:
- To elucidate the role of conserved residues in the extracellular domains of APJR in ligand binding and receptor activation.
- To investigate the impact of specific mutations on G protein (Gq, Gi) and β-arrestin-mediated signaling pathways.
Main Methods:
- Identification of conserved residues in APJR extracellular domains through multiple sequence alignment.
- Site-directed mutagenesis (alanine substitution) of identified residues.
- Assessment of ligand binding affinity and evaluation of Gq, Gi, and β-arrestin signaling activities for mutant receptors.
Main Results:
- Mutations in ECL2 (W197A) and ECL3 (L276A/L277A/W279A) significantly impaired Gi and β-arrestin signaling while largely preserving Gq signaling.
- Mutations T169A/T170A, Y182A, and T190A in ECL2 disrupted β-arrestin-dependent signaling but maintained G protein-mediated signaling.
- Structural comparisons with the angiotensin II type I receptor highlight the significance of ECL2 and ECL3 in APJR function.
Conclusions:
- Specific extracellular loop residues of APJR play distinct roles in modulating ligand binding and directing biased signaling outcomes.
- These findings provide critical insights into APJR's conformational dynamics and its ability to engage specific signaling pathways preferentially.
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