Molecular Modeling and In Vitro Functional Analysis of the RGS12 PDZ Domain Variant Associated with High-Penetrance...

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Bipolar disorder (BD) is a complex psychiatric condition with genetic and environmental influences.
• Forstner et al. identified 378 variants linked to familial BD, including an RGS12 R59Q mutation.
• Previous work showed RGS12 regulates kappa opioid receptors and dopamine homeostasis.

Purpose of the Study:

• To investigate the functional impact of the RGS12 R59Q mutation on its PDZ domain.
• To identify and validate new binding partners for the RGS12 PDZ domain.
• To assess how the R59Q variation affects RGS12's interaction with its ligands.

Main Methods:

• Molecular docking and surface plasmon resonance (SPR) to study protein-ligand interactions.
• Co-immunoprecipitation assays to validate binding partners.
• Molecular dynamics (MD) and AlphaFold2 modeling to predict structural effects.

Main Results:

• Validated SAPAP3 C-terminus as a novel binding target for the wildtype RGS12 PDZ domain.
• SPR revealed significantly reduced binding affinity of RGS12 for tested peptide targets with the R59Q mutation.
• AlphaFold2 models indicated a modest decrease in protein-peptide interactions due to the R59Q variation.

Conclusions:

• The RGS12 R59Q mutation likely weakens the protein's affinity for its in vivo targets through allosteric changes.
• This altered binding may disrupt central nervous system signaling involving dynorphin and dopamine.
• The findings suggest a potential mechanism linking the RGS12 R59Q variation to bipolar disorder pathophysiology.