Serotonin transporter (SLC6A4) allosteric S2 site (SERT S2 site)

The serotonin transporter (SERT) allosteric S2 site is a secondary binding pocket located within the extracellular vestibule of the SLC6A4 protein, distinct from the primary orthosteric (S1) site where serotonin and most antidepressants bind (Chen et al., 2005, J. Biol. Chem.). This site serves as a regulatory domain that, when occupied, induces a conformational change in the transporter that stabilizes the ligand bound at the S1 site (Plenge et al., 2007, Eur. Neuropsychopharmacol.). Specifically, the binding of drugs like escitalopram to the S2 site slows the dissociation rate of the drug from the S1 site, effectively locking the transporter in an inactive state for a longer duration (Zhong et al., 2012, Nature). This mechanism enhances the inhibition of serotonin reuptake from the synaptic cleft, thereby increasing the availability of serotonin for neurotransmission (UniProt P31645). The S2 site is a critical focus in neuropsychopharmacology for treating major depressive disorder and various anxiety disorders (Nutti et al., 2011, CNS Drugs). Research into this site has provided insights into the structural dynamics of the solute carrier 6 (SLC6) family and has facilitated the development of more potent and selective antidepressants. By modulating the kinetics of the transporter rather than just competing for the primary binding site, the S2 site offers a unique pathway for therapeutic intervention in mood disorders.

Other names

Secondary binding site of SERTAllosteric site of SLC6A4S2 binding siteExtracellular vestibule binding site

Binding to the S2 site induces a conformational change that stabilizes the ligand bound at the orthosteric (S1) site, thereby slowing its dissociation and prolonging the inhibition of serotonin reuptake (Chen et al., 2005, J. Biol. Chem.).