Ric8 proteins as the neomorphic partners of Gαo inGNAO1encephalopathies

GNAO1 mutated in pediatric encephalopathies encodes the major neuronal G-protein Gαo. Of >40 pathogenic mutations, most are single amino acid substitutions spreading across Gαo sequence. We perform extensive characterization of Gαo mutants showing abnormal GTP uptake and hydrolysis, and deficiencies to bind Gβγ and RGS19. Plasma membrane localization of Gαo is decreased for a subset of mutations that leads to epileptic manifestations. Pathogenic mutants massively gain interaction with Ric8A/B proteins, delocalizing them from cytoplasm to Golgi. Being general Gα-subunit chaperones and binding multiple other proteins, Ric8A/B likely mediate the disease dominance when engaging in neomorphic interactions with pathogenic Gαo. As the strength of Gαo-Ric8B interactions correlates with disease severity, our study further identifies an efficient biomarker and predictor for clinical manifestations in GNAO1 encephalopathies. One-Sentence Summary Neomorphic mutations in Gαo gain dominant interactions with Ric8A/B, correlating with severity in pediatric encephalopathies.