{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nThe glycine transporter 1 (GlyT1), encoded by the SLC6A9 gene, is a sodium‐ and chloride‐dependent transporter that plays a critical role in regulating extracellular glycine levels in the central nervous system. By mediating the reuptake of glycine from the synaptic cleft, GlyT1 not only terminates inhibitory glycinergic neurotransmission but also modulates the activation of N‐methyl‑D‑aspartate (NMDA) receptors, for which glycine serves as an indispensable co‐agonist. Structural studies – including high‑resolution and cryo‑EM analyses – have revealed distinct conformational states of GlyT1 involved in substrate binding and ion coupling, which are essential for its transport cycle and pharmacological inhibition."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nPharmacological interrogation of GlyT1 has further demonstrated its pivotal regulatory role in neurotransmission. Studies using glycine reuptake inhibitors in both preclinical and clinical settings have delineated how increasing synaptic glycine availability can enhance NMDA receptor function, informing therapeutic avenues for conditions such as schizophrenia and cognitive deficits. Positron emission tomography (PET) imaging assessments and occupancy models have characterized the concentration‑occupancy relationship of GlyT1 inhibitors, while reviews of NMDA receptor modulation underscore the importance of GlyT1 in shaping synaptic glycine dynamics."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nDisrupted GlyT1 function has also been linked to several neurological syndromes and developmental disorders. Experimental rodent models of temporal lobe epilepsy have revealed an overexpression of GlyT1 in the hippocampal formation, suggesting that aberrant glycine homeostasis contributes to seizure susceptibility. In humans, truncating and missense mutations in SLC6A9 underlie distinct encephalopathies—including GlyT1 encephalopathy and forms of non‑ketotic hyperglycinemia—where markedly impaired transporter activity leads to elevated cerebrospinal fluid glycine levels and severe neurodevelopmental impairment."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "8", "end_ref": "12"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nGenetic studies have explored the potential contribution of SLC6A9 variants to neuropsychiatric and substance use disorders. While some investigations have implicated specific polymorphisms in susceptibility to disorders such as methamphetamine dependence and psychosis, other studies—including those employing different population cohorts—have provided contrasting evidence regarding any significant association with schizophrenia. Combined with broader analyses in substance abuse, these findings suggest that functional variants in GlyT1 could modulate vulnerability to various neuropsychiatric conditions, even as protective effects have been proposed in certain contexts."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "13", "end_ref": "19"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its central role in neurotransmission, GlyT1 also contributes to peripheral cellular functions. For instance, in the intestine, GlyT1 mediates a substantial fraction of glycine uptake in epithelial cells, thus participating in cytoprotection and anti‑inflammatory responses. In addition, studies have noted that the localization of GlyT1 within cholesterol‑rich membrane rafts can impact its transport efficiency, while emerging evidence hints at a potential involvement in blood pressure regulation and a unique sensitivity to natural alkaloids mediated by specific cysteine residues."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "20", "end_ref": "23"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Azadeh Shahsavar, Peter Stohler, Gleb Bourenkov, et al. 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