GABA Transporters and L-type Amino Acid Transporter 1 Molecular mechanisms and transport modulation of two solute carrier families in pathophysiology

GABA transporter 1 (GAT1) and L-type amino acid transporter 1 (LAT1) are secondary transporters belonging to the solute carrier (SLC) families 6 and 7, respectively. GAT1 is a monomeric sodium dependent symporter playing a crucial role in regulating GABA concentrations within the synaptic cleft. Recent findings indicated that GAT1 interacts and transport betaine, a methylammonium solute usually transported by Betaine/GABA Transporter 1 (BGT1). The molecular mechanism, however, remains unknown. To understand the specificity and characteristics of betaine transport in GAT1 and BGT1, we identified three residues in GAT1 (Ser133, Leu300, and G403) that align with three residues in BGT1 (Glu126, Gln299, and Cys402) that might account for the differences observed between the two transporters. We revealed that GAT1 L300Q has a BGT1-like kinetics, highlighting the crucial role of a third sodium ion in BGT1 for promoting the inward-open state. Conversely, we showed that betaine reduces the affinity for sodium in GAT1 WT and L300Q indicating a transport highly sodium dependent. We propose that osmotic stress facilitates betaine transport in the GABA transporter family, a mechanism conserved from the ancestral BetP, an obligate betaine transporter from Corynebacterium glutamicum. The SLC7 transporter LAT1 is associated with the type II transmembrane protein CD98 from the SLC3 family. The heterodimer is a sodium independent amino acid antiporter and mainly expresses in cancer cells, enhancing their survival and proliferation. Thus, it is a highly relevant target in pharmacology. The LAT1 inhibitor Brasilicardin A is a diterpenoid isolated from Nocardia brasiliensis and has low toxicity and a potent IC50. However, its interaction mode with LAT1 is still unknown. Therefore, LAT1 complex was expressed and purified in order to determine its structure with BraA. This is a crucial step for identifying rudimentary functional groups to simplify the molecule synthesis. LAT1 was detected at the surface of PC-3M cells, that are ex vivo prostatic bone metastasis (BM). These hormone refractory cells are drug-resistant, however BraA represents a promising molecule to eradicate the proliferation of BM in vitro. Our findings provide new insights into the molecular mechanisms that modulate the activity of two distinct solute carrier families, opening up promising avenues for therapeutic intervention in various diseases.