Overview of the structure and function of the dopamine transporter and its protein interactions

Abstract

The dopamine transporter (DAT) plays an integral role in dopamine neurotransmission through the clearance of dopamine from the extracellular space. Dysregulation of DAT is central to the pathophysiology of numerous neuropsychiatric disorders and as such is an attractive therapeutic target. DAT belongs to the solute carrier family 6 (SLC6) class of Na+/Cl− dependent transporters that move various cargo into neurons against their concentration gradient. This review focuses on DAT (SCL6A3 protein) while extending the narrative to the closely related transporters for serotonin and norepinephrine where needed for comparison or functional relevance. Cloning and site-directed mutagenesis experiments provided early structural knowledge of DAT but our contemporary understanding was achieved through a combination of crystallization of the related bacterial transporter LeuT, homology modeling, and subsequently the crystallization of drosophila DAT. These seminal findings enabled a better understanding of the conformational states involved in the transport of substrate, subsequently aiding state-specific drug design. Post-translational modifications to DAT such as phosphorylation, palmitoylation, ubiquitination also influence the plasma membrane localization and kinetics. Substrates and drugs can interact with multiple sites within DAT including the primary S1 and S2 sites involved in dopamine binding and novel allosteric sites. Major research has centered around the question what determines the substrate and inhibitor selectivity of DAT in comparison to serotonin and norepinephrine transporters. DAT has been implicated in many neurological disorders and may play a role in the pathology of HIV and Parkinson’s disease via direct physical interaction with HIV-1 Tat and α-synuclein proteins respectively.

Computational Chemistry in Structure-Based Solute Carrier Transporter Drug Design: Recent Advances and Future Perspectives

“…Since 2005, the first X-ray crystal structure (PDB ID: 2A65) of the bacterial leucine transporter (LeuT) was reported, and the structures of the LeuT, drosophila dopamine transporter (dDAT), and SERT have been used as templates for the construction of structural models of MATs. ,, Fu et al also modeled a large number of structural variabilities of SCLs by homology modeling and added them to the VARIDT database () . Recently, the popular AI protein structure prediction method AlphaFold2 can also be used to accurately predict transporter structures. , These structural models obtained by computational techniques greatly enrich the structural information on SLCs and are widely used in drug design and transport mechanism studies. ,− Nevertheless, the application of computational structures in drug design still faces several challenges; the accuracy of models and diversity of conformations need to be carefully considered . Considering that conformational changes of proteins are closely related to their function, studying the multiple conformations of SLCs is helpful to understand their transport mechanism.…”

Assessment of the relationship between the dopaminergic pathway and severe acute respiratory syndrome coronavirus 2 infection, with related neuropathological features, and potential therapeutic approaches in COVID‐19 infection

“…In areas with low concentrations of dopamine transporters, the norepinephrine transporter can also take up dopamine. 49,50 The vesicular monoamine transporter 2 (VMAT2) in vesicular membranes transports dopamine from the cytoplasm back into the neuron. To inactivate dopamine remaining in the cytoplasm, monoamine oxidase (MAO) and Omethylation by catechol-O-methyl transferase (COMT) are involved, producing dihydroxyphenylacetic acid and homovanillic acid.…”

“…When neurons are excited, dopamine is released into the synaptic cleft, which can be reabsorbed by the dopamine transporter (DAT) at the presynaptic membrane. In areas with low concentrations of dopamine transporters, the norepinephrine transporter can also take up dopamine 49,50 . The vesicular monoamine transporter 2 (VMAT2) in vesicular membranes transports dopamine from the cytoplasm back into the neuron.…”

Leaky lessons learned: Efflux prone dopamine transporter variant reveals sex and circuit specific contributions of D2 receptor signalling to neuropsychiatric disease

“…In the CNS, DAT is expressed on DAergic neurons and predominantly localizes to extrasynaptic or perisynaptic compartments, a pattern that also applies to DA receptors, which supports the concept that DA neurotransmission can be classified as diffusion‐based volume transmission 11,39 with the density of DAT expressing axons and the density of DAT per axon determining the spread of DA after release. Structurally, DAT is comprised of 12 membrane‐spanning domains (TMDs) with a large extracellular loop between TMDs 3 and 4 that bears N‐linked glycosylation 11,40,41 . The intracellular carboxy‐ and amino termini harbour multiple regulatory sites for regulatory post‐translational modifications and support protein–protein interactions that allow for ample and complex regulatory processes, 42,43 whose extent and dynamics are still under investigation.…”

“…Structurally, DAT is comprised of 12 membrane-spanning domains (TMDs) with a large extracellular loop between TMDs 3 and 4 that bears N-linked glycosylation. 11,40,41 The intracellular carboxyand amino termini harbour multiple regulatory sites for regulatory post-translational modifications and support protein-protein interactions that allow for ample and complex regulatory processes, 42,43 whose extent and dynamics are still under investigation. As a member of the solute carrier 6 (SLC6) family, DAT operates as a neurotransmitter: a sodium symporter where the concentrative power of DAT relies on the coupling of an energetically favourable translocation of sodium to the inward transport of extracellular DA.…”