Structural basis of organic cation transporter-3 inhibition

Abstract

Organic cation transporters (OCTs) facilitate the translocation of catecholamines, drugs and xenobiotics across the plasma membrane in various tissues throughout the human body. OCT3 plays a key role in low-affinity, high-capacity uptake of monoamines in most tissues including heart, brain and liver. Its deregulation plays a role in diseases. Despite its importance, the structural basis of OCT3 function and its inhibition has remained enigmatic. Here we describe the cryo-EM structure of human OCT3 at 3.2 Å resolution. Structures of OCT3 bound to two inhibitors, corticosterone and decynium-22, define the ligand binding pocket and reveal common features of major facilitator transporter inhibitors. In addition, we relate the functional characteristics of an extensive collection of previously uncharacterized human genetic variants to structural features, thereby providing a basis for understanding the impact of OCT3 polymorphisms.

Stereoselectivity in Cell Uptake by SLC22 Organic Cation Transporters 1, 2, and 3

“…All prominent differences in transport kinetics identified here were differences in the maximum transport rate (Figures , , and and Table S1). Although with the recent cryo-EM data, ,, we have much better structural insights into the OCTs than before, we still do not understand all aspects of the transport processes. We may speculate that the maximum transport rate is not (or not only) correlated with a high binding affinity to the transporter in the outward-open configuration but with rapid substrate release from the inward-open configuration.…”

“…However, mutagenesis studies of OCT1 demonstrated that single amino acids can completely determine a transporters’ stereoselectivity . Although this has not been shown for OCT2 and OCT3 yet, the revolution of structural biology by the improvements in cryogenic electron microscopy (cryo-EM) has just affected the OCT field. , High-resolution structural data might accelerate the identification of amino acids determining the stereoselectivity of OCT2 and OCT3 by computationally guided biochemical studies. The frequent naturally occurring genetic variants studied here did not affect the transporters’ stereoselectivity.…”

“…Zolmitriptan is used as the pure ( S )-enantiomer, which is extensively transported by OCT3 (Figure ). Thus, for instance, interactions at OCT3 or the rare genetic polymorphisms of OCT3 may have clinical relevance in certain drug combinations or in carriers of the more rare OCT3 genetic polymorphisms. Reasons for marketing ( R )-frovatriptan and ( S )-zolmitriptan are not fully disclosed, but ( S )-zolmitriptan may have a moderately higher 5HT1D receptor binding than the ( R )-enantiomer .…”

“…The functional consequences range from a reduced function to a complete loss of function and may be relevant for the pharmacokinetics of several drugs. − OCT2 has one frequent polymorphism (Ala270Ser) which only leads to moderate impairment of transporter function . Also in OCT3, several heritable variants have been recently described and are possibly associated with psychiatric diseases . Although this may highlight the role of OCT3 in brain cation homeostasis, the allele frequencies of these variants are probably too low to have broad, population-relevant pharmacokinetic effects.…”

Serotonin-releasing agents with reduced off-target effects

“…Confocal microscopy and image analysis. Confocal microscopy and image analysis was conducted as previously described [32]. In brief, cells expressing yellow fluorescent protein(YFP)-tagged human SERT or DAT, respectively, were seeded on PDL-coated 35 mm glass-bottom dishes 24 h before image acquisition.…”