Substrate recognition and translocation by polyspecific organic cation transporters

2011 ◽  
Vol 392 (1-2) ◽  
Author(s):  
Hermann Koepsell
Keyword(s):  
Conformational Changes ◽  
Binding Sites ◽  
Organic Cation ◽  
Substrate Binding ◽  
Substrate Recognition ◽  
Organic Cation Transporters ◽  
Cationic Drugs ◽  
High Affinity ◽  
Cation Transporters ◽  
Substrate Binding Sites

Abstract Organic cation transporters (OCTs) of the SLC22 family play a pivotal role in distribution and excretion of cationic drugs. They mediate electrogenic translocation of cations in both directions. OCTs are polyspecific transporters. During substrate translocation they perform a series of conformational changes involving an outward-facing conformation, an occluded state and an inward-facing conformation. Mutagenesis of OCT1 in combination with homology modeling showed that identical amino acids form the innermost parts of the outward-open and inward-open binding clefts. In addition to low affinity substrate binding sites, OCT1 contains high affinity substrate binding sites that can mediate inhibition via non-transported compounds.

Multiple binding sites in organic cation transporters require sophisticated procedures to identify interactions of novel drugs

2019 ◽  
Vol 400 (2) ◽  
pp. 195-207 ◽  
Author(s):  
Hermann Koepsell
Keyword(s):  
Binding Sites ◽  
Organic Cation ◽  
Cation Binding ◽  
Organic Cation Transporters ◽  
High Affinity ◽  
Multiple Binding Sites ◽  
Novel Drugs ◽  
Cation Transporters ◽  
Influence Of Substrate

AbstractIn vitroevaluation of drugs for interaction with transporters is essential during drug development. As polyspecific organic cation transporters (OCTs) are critical for pharmacokinetics of many cationic drugs,in vitrotesting of human OCT1 and human OCT2 is recommended. In the currently applied tests it is determined whether uptake of one model cation in stably transfected epithelial cells is inhibited using a substrate concentration in the micromolar range. In this review experimental evidence for the existence of low- and high-affinity cation binding sites in OCTs that may interact with drugs is compiled. Most data were obtained from studies performed with rat Oct1. Whereas overlapping low-affinity cation binding sites are directly involved in transport, the high-affinity cation binding sites may induce allosteric inhibition of transport. Remarkably, high-affinity inhibition is only observed when uptake is measured using nanomolar substrate concentrations far below the respectiveKmvalues. Affinities of inhibitors are dependent on molecular structure and concentration of the employed substrate. Because the currently appliedin vitrotests for identification of interaction of novel drugs with OCTs do not consider the influence of substrate structure and are not capable of identifying high-affinity inhibition, more sophisticated testing protocols are proposed.

scholarly journals To be, or not to be two sites: that is the question about LeuT substrate binding

2011 ◽  
Vol 138 (4) ◽  
pp. 467-471 ◽  
Author(s):  
Nicolas Reyes ◽  
Sotiria Tavoulari
Keyword(s):  
Binding Sites ◽  
Journal Club ◽  
Substrate Binding ◽  
Structural Data ◽  
Transport Proteins ◽  
Model System ◽  
Transport Mechanisms ◽  
High Affinity ◽  
The Central Nervous System ◽  
Substrate Binding Sites

Transport proteins of the neurotransmitter sodium symporter (NSS) family regulate the extracellular concentration of several neurotransmitters in the central nervous system. The only member of this family for which atomic-resolution structural data are available is the prokaryotic homologue LeuT. This protein has been used as a model system to study the molecular mechanism of transport of the NSS family. In this Journal Club, we discuss two strikingly different LeuT transport mechanisms: one involving a single high-affinity substrate binding site and one recently proposed alternative involving two high-affinity substrate binding sites that are allosterically coupled.

Organic cation transporters OCT1, 2, and 3 mediate high-affinity transport of the mutagenic vital dye ethidium in the kidney proximal tubule

2009 ◽  
Vol 296 (6) ◽  
pp. F1504-F1513 ◽  
Author(s):  
Wing-Kee Lee ◽  
Markus Reichold ◽  
Bayram Edemir ◽  
Giuliano Ciarimboli ◽  
Richard Warth ◽  
...  
Keyword(s):  
Organic Cation ◽  
Fluorescent Dyes ◽  
Mouse Kidney ◽  
Proximal Tubules ◽  
Facilitated Diffusion ◽  
Organic Cation Transporters ◽  
High Affinity ◽  
Cation Transporters ◽  
Safety Guidelines ◽  
Positively Charged

The positively charged fluorescent dyes ethidium (Et+) and propidium (Pr2+) are widely used as DNA and necrosis markers. Et+is cytotoxic and mutagenic. The polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3) mediate electrogenic facilitated diffusion of small (≤500 Da) organic cations with broad specificities. In humans, OCT2 mediates basolateral uptake by kidney proximal tubules (PT), whereas in rodents OCT1/2 are involved. In mouse kidney, perfused Et+accumulated predominantly in the S2/S3 segments of the PT, but not Pr2+. In cells stably overexpressing human OCTs (hOCTs), Et+uptake was observed with Kmvalues of 0.8 ± 0.2 μM (hOCT1), 1.7 ± 0.5 μM (hOCT2), and 2.0 ± 0.5 μM (hOCT3), whereas Pr2+was not transported. Accumulation of Et+was inhibited by OCT substrates quinine, 3-methyl-4-phenylpyridinium (MPP+), cimetidine, and tetraethylammonium (TEA+). For hOCT1 and hOCT2, the IC50values for MPP+, TEA+, and cimetidine were higher than for inhibition of previously tested transported substrates. For hOCT2, the inhibition of Et+uptake by MPP+and cimetidine was shown to be competitive. Et+also inhibited transport of 0.1 μM [3H]MPP+by all hOCT isoforms with IC50values between 0.4 and 1.3 μM, and the inhibition of hOCT1-mediated uptake of MPP+by Et+was competitive. In Oct1/2−/−mice, Et+uptake in the PT was almost abolished. The data demonstrate that Et+is taken up avidly by the PT, which is mediated by OCT1 and/or OCT2. Considering the high affinity of OCTs for Et+and their strong expression in various organs, strict safety guidelines for Et+handling should be reinforced.

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