Sodium-dependent serotonin transporter (SERT) allosteric site (SERT allosteric site)

The allosteric site of the serotonin transporter (SERT), frequently referred to as the S2 site, is a secondary binding pocket located in the extracellular vestibule of the protein, separate from the central orthosteric (S1) site where serotonin and most selective serotonin reuptake inhibitors (SSRIs) bind [1, 5]. While the S1 site is the primary locus for inhibiting serotonin reuptake, the allosteric site functions as a regulatory region that can modulate the affinity and dissociation kinetics of ligands at the primary site [3, 6]. For example, the antidepressant escitalopram binds to both sites; its occupancy of the allosteric site induces a conformational change that locks the drug into the orthosteric site, significantly slowing its dissociation and enhancing its inhibitory effect on serotonin transport [4, 8]. This unique dual-binding mechanism is believed to contribute to the superior clinical efficacy and faster onset of action observed with escitalopram compared to other antidepressants [1, 2]. The allosteric site is increasingly recognized as a viable target for the design of novel, high-affinity modulators that can fine-tune serotonergic signaling in the treatment of major depressive disorder, anxiety, and other neuropsychiatric conditions [11, 13]. Structural studies have localized this site to a region formed by extracellular loops and transmembrane helices, distinct from the substrate translocation pathway [8, 9]. Research into allosteric modulators like Lu AF60097 and ATM7 aims to develop therapies with improved safety profiles and efficacy by targeting this specific regulatory mechanism [11, 14].

Other names

S2 siteSecondary binding siteVestibular binding siteLow-affinity binding siteSLC6A4 allosteric site

Allosteric modulation of the orthosteric (S1) binding site, which stabilizes ligand binding and slows the dissociation rate of inhibitors, thereby enhancing the inhibition of serotonin reuptake.