Structural mechanisms for VMAT2 inhibition by tetrabenazine

Structure and mechanism of human vesicular polyamine transporter

Polyamines play essential roles in gene expression and modulate neuronal transmission in mammals. Vesicular polyamine transporters (VPAT) from the SLC18 family exploit the transmembrane H+ gradient to translocate polyamines into secretory vesicles, enabling the quantal release of polyamine neuromodulators and underpinning learning and memory formation. Here, we report the cryo-electron microscopy structures of human VPAT in complex with spermine, spermidine, H+, or tetrabenazine, elucidating discrete lumen-facing states of the antiporter and pivotal interactions between VPAT and its substrate or inhibitor. Leveraging structure-inspired mutagenesis studies and protein structure prediction, we deduce an unforeseen mechanism whereby the polyamine and H+ compete for multiple acidic protein residues both directly and indirectly, and rationalize how the antidopaminergic therapeutic tetrabenazine impedes vesicular transport of polyamines. This study unravels the mechanism of an H+-coupled polyamine antiporter, reveals mechanistic diversity between VPAT and other SLC18 antiporters, and raises new prospects for combating human disorders of polyamine homeostasis.

Structural Basis for Inhibition of Urate Reabsorption in URAT1

The urate transporter 1 (URAT1) is the primary urate transporter in the kidney responsible for urate reabsorption and, therefore, is crucial for urate homeostasis. Hyperuricemia causes the common human disease gout and other pathological consequences. Inhibition of urate reabsorption through URAT1 has been shown as a promising strategy in alleviating hyperuricemia, and clinical and preclinical drug candidates targeting URAT1 are emerging. However, how small molecules inhibit URAT1 remains undefined, and the lack of accurate URAT1 complex structures hinders the development of better therapeutics. Here, we present cryoelectron microscopy structures of a humanized rat URAT1 bound with benzbromarone, lingdolinurad, and verinurad, elucidating the structural basis for drug recognition and inhibition. The three small molecules reside in the URAT1 central cavity with different binding modes, locking URAT1 in an inward-facing conformation. This study provides mechanistic insights into the drug modulation of URAT1 and sheds light on the rational design of potential URAT1-specific therapeutics for treating hyperuricemia.

ATP-Binding Cassette and Solute Carrier Transporters: Understanding Their Mechanisms and Drug Modulation Through Structural and Modeling Approaches

The ATP-binding cassette (ABC) and solute carrier (SLC) transporters play pivotal roles in cellular transport mechanisms, influencing a wide range of physiological processes and impacting various medical conditions. Recent advancements in structural biology and computational modeling have provided significant insights into their function and regulation. This review provides an overview of the current knowledge of human ABC and SLC transporters, emphasizing their structural and functional relationships, transport mechanisms, and the contribution of computational approaches to their understanding. Current challenges and promising future research and methodological directions are also discussed.