DIFFERENTIAL MODULATION OF GLYRΑ3 BY SEC8 PROTEIN: IMPACT OF PHOSPHORYLATION OF RESIDUE S346 ON THE INTERACTION OF SEC8 WITH THE GLYRΑ3

The glycine receptor (GlyR) is a chloride ion channel from the pentameric ligand-gated ion channel (pLGIC) family, which includes nicotinic acetylcholine, serotonin type 3, and GABA type A receptors. GlyRs regulate neuronal excitability in the central nervous system (CNS), and their dysfunction is linked to hyperekplexia, autism, schizophrenia, epilepsy, and chronic pain. GlyRs consist of four α subunits (α1–α4) and one β subunit, each with an extracellular domain (ECD), transmembrane domain (TMD), and intracellular domain (ICD). The function of GlyRs can be modulated by external or endogenous allosteric modulators, and intracellular protein interactions or PKA mediated phosphorylation events also allosterically influence GlyR function. The α3 subunit is enriched in the dorsal horn of the spinal cord and is involved in sensory processing, particularly nociceptive signaling. Notably, phosphorylation of residue S346 in the ICD of GlyRα3 has been linked to chronic pain. SEC8, a protein involved in the secretory pathway, interacts with the GlyRα3 ICD, but its effect on GlyR function, particularly in the phosphorylated state, remains unclear. Using biochemical, bioinformatic, and electrophysiological techniques, we investigated the GlyRα3–SEC8 interaction. Our results show that SEC8 differentially modulates glycine-activated currents in wild-type GlyRα3 and the S346E phosphomimetic variant. At the single channel level, SEC8 prolonged open times and increased amplitude. These findings suggest a selective positive modulation of the phosphomimetic receptor by SEC8, highlighting the ICD as a potential therapeutic target for GlyR dysfunction-related disorders.