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Updated: Jan 10, 2026
11:34
Exploring Sequence Space to Identify Binding Sites for Regulatory RNA-Binding Proteins
Published on: August 9, 2019
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Structural basis of modified ligand selectivity from N-terminal PAC1R alternative splicing
Jessica J Lu1,2, Giuseppe Deganutti3, Miaomiao Li1,2
1Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia.
Summary
The pituitary adenylate cyclase-activating polypeptide 1 receptor (PAC1R) short variant (PAC1sR) shows enhanced VIP activity due to structural differences in its extracellular domain (ECD) compared to the null variant (PAC1nR). This splicing impacts ligand binding and G protein signaling.
Area of Science:
- Molecular pharmacology
- Structural biology
- G protein-coupled receptor research
Background:
- The pituitary adenylate cyclase-activating polypeptide 1 receptor (PAC1R) is a class B1 GPCR activated by PACAP and VIP.
- Alternate splicing generates PAC1R short (PAC1sR) and null (PAC1nR) variants with distinct functional properties.
- Understanding how ECD splicing affects PAC1R function and ligand selectivity is crucial.
Purpose of the Study:
- To pharmacologically characterize and structurally elucidate the functional differences between PAC1sR and PAC1nR.
- To investigate the mechanistic basis for enhanced VIP activity at PAC1sR.
- To understand the impact of ECD splicing on PAC1R ligand engagement and downstream signaling.
Main Methods:
- Comprehensive functional assays to assess signaling outcomes of PAC1sR and PAC1nR activation.
- Cryo-electron microscopy (Cryo-EM) to determine the structures of VIP-bound PAC1sR and PAC1nR.
- Molecular dynamics (MD) simulations to analyze ligand-receptor and receptor-G protein interactions.
Main Results:
- VIP, but not PACAP, exhibited globally enhanced activity at PAC1sR compared to PAC1nR across various functional endpoints.
- Cryo-EM structures revealed that PAC1nR has transient null loop engagement absent in PAC1sR, affecting VIP binding.
- MD simulations predicted differential Gs protein interactions, indicating a greater allosteric influence on VIP affinity at PAC1sR.
Conclusions:
- PAC1R ECD splicing significantly alters VIP activity and signaling profiles.
- Structural differences, particularly the null loop interaction in PAC1nR, underlie the functional divergence between PAC1sR and PAC1nR.
- This study provides structural insights into PAC1R ligand selectivity and signaling, driven by alternative splicing.
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