Serotonin Transporters (SERTs) are integral membrane proteins that transport serotonin from synaptic spaces into presynaptic neurons. SERTs function by reuptaking serotonin in the synaptic cleft, effectively terminating the function of serotonin and halting neuronal transmission. Serotonin reuptake is a critical process to prevent overstimulation of nerves.

Serotonin transporter (SERT) regulates extracellular levels of serotonin (5-hydroxytryptamine, 5HT) in the brain by transporting 5HT into neurons and glial cells. The human SERT (hSERT) is the primary target for drugs used in the treatment of emotional disorders, including depression. hSERT belongs to the solute carrier 6 family that includes a bacterial leucine transporter (LeuT), for which a high resolution crystal structure has become available.