Sodium-dependent serotonin transporter (SLC6A4) secondary allosteric site (SERT secondary allosteric site)

The secondary allosteric site on the serotonin transporter (SLC6A4) is a distinct binding pocket located in the extracellular vestibule, separate from the central orthosteric substrate-binding site (Coleman et al., 2016, Nature). While the primary site is where serotonin and most selective serotonin reuptake inhibitors (SSRIs) bind to block transport, the allosteric site serves as a regulatory region that can modulate the affinity and dissociation rate of ligands at the primary site (Plenge et al., 2007, Eur Neuropsychopharmacol). Escitalopram is the most notable drug that utilizes this site; by binding to the allosteric pocket, it sterically hinders the exit of the drug molecule already bound in the orthosteric site, effectively "locking" it in place and enhancing the duration of transporter inhibition (Chen et al., 2005, J Neurochem). This mechanism contributes to the high potency and clinical efficacy of escitalopram in treating major depressive disorder and various anxiety disorders (Zhong et al., 2012, Bioorg Med Chem Lett). Understanding this site has provided critical insights into the structural biology of neurotransmitter transporters and the development of more effective antidepressants (UniProt P31645).

Other names

S-siteAllosteric site of SERTSecondary binding site of SLC6A4Extracellular vestibule allosteric site

Allosteric modulation of the serotonin transporter; binding to this site decreases the dissociation rate of ligands from the primary orthosteric site, thereby prolonging the inhibition of serotonin reuptake.