Redox-dependent synaptic clustering of gephyrin

Reactive oxygen species (ROS) play a central role in enhancing inhibitory signal transmission, thus extending their role beyond oxidative stress in disease and aging. However, the underlying molecular mechanisms mediating these functions have remained elusive. At inhibitory synapses, the scaffolding protein gephyrin clusters glycine and GABA type A receptors. Since gephyrin harbors multiple surface-exposed cysteines, we investigated the regulatory influence of ROS on gephyrin. We show that H2O2-induced oxidation of gephyrin cysteines triggered reversible, synaptic multimerization through disulfide bridge formation, which provided more receptor binding sites, lead to proteolytic protection and enhanced liquid-liquid phase separation. We identified mitochondria-derived ROS as a physiological source and observed oxidized gephyrin multimers in vivo, indicating that gephyrin can be regulated by the redox environment. Collectively, our findings suggest that cysteines in gephyrin modulate synaptic localization and clustering as regulatory redox-switches thereby establishing a link between neuronal and mitochondrial activity. ### Competing Interest Statement The authors have declared no competing interest.