Deciphering the Molecular Mechanisms of Startle Disease: the Role of the N46K Mutation in the Glycine Receptor

The glycine receptor (GlyR) is a pentameric ligand-gated ion channel that plays important physiological roles in the nervous system. Its malfunction is related to neurological disorders including startle disease (hyperekplexia), which is characterized by exaggerated startle responses to sudden unexpected stimuli, such as noise or touch. Here, we unravel the molecular mechanisms of action of a specific mutation that is linked to startle disease: N46K. This residue, in the GlyR extracellular domain, is not directly involved in neurotransmitter binding but can disrupt the neurotransmitter pathway. To understand how, we performed molecular dynamics simulations of the wild-type and mutated extracellular domain of a homomeric α-1 GlyR, assessing the effects of the N46K mutation. We then sampled multiple unbinding and binding events by means of metadynamics simulations, with a funnel restraint to limit the exploration in the solvent. By evaluating the binding free energy landscape, we observed a substantial reduction in neurotransmitter binding affinity, which is consistent with experiments. We suggest that such reduction is linked to the interaction of its crucial glutamic acid residue with the lysine mutation competing with the glycine ligand.