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.

scholarly journals Oligomerization of a molecular chaperone modulates its activity

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Tomohide Saio ◽  
Soichiro Kawagoe ◽  
Koichiro Ishimori ◽  
Charalampos G Kalodimos
Keyword(s):  
Binding Sites ◽  
Substrate Binding ◽  
Structural Data ◽  
Trigger Factor ◽  
Unfolded Proteins ◽  
Protein Substrates ◽  
Native Proteins ◽  
Dimeric Interface ◽  
Substrate Binding Sites ◽  
Resolution Structure

Molecular chaperones alter the folding properties of cellular proteins via mechanisms that are not well understood. Here, we show that Trigger Factor (TF), an ATP-independent chaperone, exerts strikingly contrasting effects on the folding of non-native proteins as it transitions between a monomeric and a dimeric state. We used NMR spectroscopy to determine the atomic resolution structure of the 100 kDa dimeric TF. The structural data show that some of the substrate-binding sites are buried in the dimeric interface, explaining the lower affinity for protein substrates of the dimeric compared to the monomeric TF. Surprisingly, the dimeric TF associates faster with proteins and it exhibits stronger anti-aggregation and holdase activity than the monomeric TF. The structural data show that the dimer assembles in a way that substrate-binding sites in the two subunits form a large contiguous surface inside a cavity, thus accounting for the observed accelerated association with unfolded proteins. Our results demonstrate how the activity of a chaperone can be modulated to provide distinct functional outcomes in the cell.

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.

Substrate-binding sites in acetylcholinesterase

1991 ◽  
Vol 12 ◽  
pp. 422-426 ◽  
Author(s):  
Ferdinand Hucko ◽  
Jaak Järv ◽  
Christoph Weise
Keyword(s):  
Binding Sites ◽  
Substrate Binding ◽  
Substrate Binding Sites

scholarly journals Human organic anion transporter MRP4 (ABCC4) is an efflux pump for the purine end metabolite urate with multiple allosteric substrate binding sites

2005 ◽  
Vol 288 (2) ◽  
pp. F327-F333 ◽  
Author(s):  
Rémon A. M. H. Van Aubel ◽  
Pascal H. E. Smeets ◽  
Jeroen J. M. W. van den Heuvel ◽  
Frans G. M. Russel
Keyword(s):  
Binding Sites ◽  
Efflux Pump ◽  
Substrate Binding ◽  
Organic Anion ◽  
Apical Cell ◽  
Cell Uptake ◽  
Hek293 Cells ◽  
Hill Coefficient ◽  
Anion Transporter ◽  
Substrate Binding Sites

The end product of human purine metabolism is urate, which is produced primarily in the liver and excreted by the kidney through a well-defined basolateral blood-to-cell uptake step. However, the apical cell-to-urine efflux mechanism is as yet unidentified. Here, we show that the renal apical organic anion efflux transporter human multidrug resistance protein 4 (MRP4), but not apical MRP2, mediates ATP-dependent urate transport via a positive cooperative mechanism ( Km of 1.5 ± 0.3 mM, Vmax of 47 ± 7 pmol·mg−1·min−1, and Hill coefficient of 1.7 ± 0.2). In HEK293 cells overexpressing MRP4, intracellular urate levels were lower than in control cells. Urate inhibited methotrexate transport (IC50 of 235 ± 8 μM) by MRP4, did not affect cAMP transport, whereas cGMP transport was stimulated. Urate shifted cGMP transport by MRP4 from positive cooperativity ( Km and Vmax value of 180 ± 20 μM and 58 ± 4 pmol·mg−1·min−1, respectively, Hill coefficient of 1.4 ± 0.1) to single binding site kinetics ( Km and Vmax value of 2.2 ± 0.9 mM and 280 ± 50 pmol·mg−1·min−1, respectively). Finally, MRP4 could transport urate simultaneously with cAMP or cGMP. We conclude that human MRP4 is a unidirectional efflux pump for urate with multiple allosteric substrate binding sites. We propose MRP4 as a candidate transporter for urinary urate excretion and suggest that MRP4 may also mediate hepatic export of urate into the circulation, because of its basolateral expression in the liver.

Chemical mechanism and substrate binding sites of NADP-dependent aldehyde dehydrogenase from Streptococcus mutans

2001 ◽  
Vol 130-132 ◽  
pp. 15-28 ◽  
Author(s):  
Stéphane Marchal ◽  
David Cobessi ◽  
Sophie Rahuel-Clermont ◽  
Frédérique Tête-Favier ◽  
André Aubry ◽  
...  
Keyword(s):  
Streptococcus Mutans ◽  
Aldehyde Dehydrogenase ◽  
Binding Sites ◽  
Substrate Binding ◽  
Chemical Mechanism ◽  
Substrate Binding Sites
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