Role of palmitoylation on the neuronal glycine transporter GlyT2

Abstract

The neuronal glycine transporter GlyT2 removes glycine from the synaptic cleft through active Na⁺, Cl⁻, and glycine cotransport contributing to the termination of the glycinergic signal as well as supplying substrate to the presynaptic terminal for the maintenance of the neurotransmitter content in synaptic vesicles. Patients with mutations in the human GlyT2 gene (SLC6A5), develop hyperekplexia or startle disease (OMIM 149400), characterized by hypertonia and exaggerated startle responses to trivial stimuli that may have lethal consequences in the neonates as a result of apnea episodes. Post-translational modifications in cysteine residues of GlyT2 are an aspect of structural interest we analyzed. Our study is compatible with a reversible and short-lived S-acylation in spinal cord membranes, detectable by biochemical and proteomics methods (acyl-Rac binding and IP-ABE) confirmed with positive and negative controls (palmitoylated and non-palmitoylated proteins). According to a short-lived modification, direct labeling using click chemistry was faint but mostly consistent. We have analyzed the physiological properties of a GlyT2 mutant lacking the cysteines with high prediction of palmitoylation and the mutant is less prone to be included in lipid rafts, an effect also observed upon treatment with the palmitoylation inhibitor 2-bromopalmitate. This work demonstrates there are determinants of lipid raft inclusion associated with the GlyT2 mutated cysteines, which are presumably modified by palmitoylation.