Multifaceted disruption of AMPA receptor signaling by CACNG8 variants: Integrated evidence from human genetics and molecular simulation

The Transmembrane AMPA Receptor Regulatory Protein Gamma-8 (TARP γ-8), encoded by <i>CACNG8</i>, regulates AMPA receptor (AMPAR) trafficking, gating, and synaptic localization. Although well-characterized in central synapses, its role in retinal development and disease remains underexplored. This study investigates <i>CACNG8</i> within the context of inherited retinal dystrophies (IRDs) by integrating human genetics within silico structural analysis. Whole Exome Sequencing (WES) was performed on IRD-affected families with atypical phenotypes-such as residual photoreceptor activity alongside severe optic atrophy or abnormal electroretinogram (ERG) profiles-yet no biallelic mutations in known IRD genes. In all families, rare heterozygous or compound heterozygous <i>CACNG8</i> variants were identified, including a recurrent stop-gain (p.Arg123Ter) and two missense variants (p.Leu96Val, p.Val102Met), suggesting a potential modifier role. To explore their functional impact, we modeled 14 AMPAR-associated postsynaptic complexes, comparing wild-type and mutant TARP γ-8 configurations. These included auxiliary subunits (CACNG2-7, CNIH2/3), scaffolding proteins (PSD93, PSD95), and regulators (PPP3CA, RIMBPs). Docking and MM-PBSA/MM-GBSA analyses revealed that truncation or destabilization of CACNG8 severely reduced complex stability (ΔΔG > 20 kcal/mol) and altered binding geometry. Molecular dynamics simulations highlighted increased structural perturbations, reduced hydrogen bonding, and greater conformational disorder in mutant assemblies. Grid Inhomogeneous Solvation Theory (GIST) and PCA/TICA analyses further revealed diminished water structuring and constrained conformational landscapes. Altogether, our findings support the potential role of <i>CACNG8</i> as a genetic modifier in IRDs, pending further validation in larger cohorts. The study illustrates how combining genomic and structural approaches can uncover hidden contributors to complex retinal disorders.