Structural basis of promiscuous substrate transport by Organic Cation Transporter 1

Abstract

Organic Cation Transporter 1 (OCT1) plays a crucial role in hepatic metabolism by mediating the uptake of a range of metabolites and drugs. Genetic variations can alter the efficacy and safety of compounds transported by OCT1, such as those used for cardiovascular, oncological, and psychological indications. Despite its importance in drug pharmacokinetics, the substrate selectivity and underlying structural mechanisms of OCT1 remain poorly understood. Here, we present cryo-EM structures of full-length human OCT1 in the inward-open conformation, both ligand-free and drug-bound, indicating the basis for its broad substrate recognition. Comparison of our structures with those of outward-open OCTs provides molecular insight into the alternating access mechanism of OCTs. We observe that hydrophobic gates stabilize the inward-facing conformation, whereas charge neutralization in the binding pocket facilitates the release of cationic substrates. These findings provide a framework for understanding the structural basis of the promiscuity of drug binding and substrate translocation in OCT1.

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.…”

“…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. Thus, for a better understanding of the enantiospecific differences of OCT2-mediated transport of fenoterol or the OCT3-mediated transport of terbutaline or zolmitriptan, we would need further experimental cryo-EM data with the enantiomers, and we would expect that there are differences in the affinity of the enantiomers to the protein in that configuration . In addition, there may be substrate-dependent differences in the translocation process.…”

“…Thus, for a better understanding of the enantiospecific differences of OCT2-mediated transport of fenoterol or the OCT3-mediated transport of terbutaline or zolmitriptan, we would need further experimental cryo-EM data with the enantiomers, and we would expect that there are differences in the affinity of the enantiomers to the protein in that configuration. 30 In addition, there may be substrate-dependent differences in the translocation process. Although the enantiomeric differences with fenoterol, terbutaline, and zolmitriptan were highly significant and around 10-fold, it is questionable whether, with these moderate differences, different binding in cryo-EM could be demonstrated.…”

Structural basis of substrate transport and drug recognition by the human thiamine transporter SLC19A3

“…The reported transport affinity of OCT1 for thiamine is much lower than for the SLC19A transporters (Km ~ 780 μM compared to 2-7 μM) [7][8][9] . This difference could be explained by a looser coordination of thiamine in OCT1, compared to the tight binding observed in hSLC19A3 40 (Supplementary Fig. 17).…”

Ianus Bifrons: The Two Faces of Metformin

“…The main mechanisms producing the anti-hyperglycemic action of metformin reside in mitochondria and lysosomes, after the interaction of metformin with organic cationic transporter 1 [57,58].…”