Substrate and inhibitor binding to the serotonin transporter: Insights from computational, crystallographic, and functional studies.

The serotonin transporter (SERT) is a monoamine transporter that regulates serotonergic signaling by reuptaking serotonin from the synaptic cleft into the presynaptic neuron. Its dysregulation is linked to major depressive disorder (MDD), a leading cause of years lived with disease in 2016. Many antidepressants target SERT, and since the first bacterial SERT homologue structure was solved in 2005, crystallographic, computational, and functional studies have advanced understanding of drug binding. This review compares findings from these methods on substrate and inhibitor binding modes, highlighting caveats of each approach. It covers binding of the cognate substrate and various antidepressants—tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, multimodal drugs—and illicit drugs like cocaine, amphetamines, and ibogaine.

Study at a glance

Abstract

The serotonin transporter (SERT) belongs to the monoamine transporter family, which also includes the dopamine and norepinephrine transporters. SERT is essential for regulating serotonergic signaling by the reuptake of serotonin from the synaptic cleft back into the presynaptic neuron. Dysregulation of SERT has been implicated in several major psychiatric disorders such as major depressive disorder (MDD). MDD was among the top five leading causes of years lived with disease in 2016 and is characterized as a major global burden. Several drugs have been developed to target SERT for use in the treatment of MDD, and their respective binding modes and locations within SERT have been studied. The elucidation of the first structure of a bacterial SERT homologue in 2005 has accelerated crystallographic, computational, and functional studies to further elucidate drug binding and method of action in SERT. Herein, we aim to highlight and compare these studies with an emphasis on what the different experimental methods conclude on substrate and inhibitor binding modes, and the potential caveats of using the different types of studies are discussed. We focus this review on the binding of cognate substrate and drugs belonging to the different families of antidepressants, including tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and multimodal drugs, as well as illicit drugs such as cocaine, amphetamines, and ibogaine. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.