Structural Biology 2018: Mechanism of a bacterial multidrug ABC (ATP-binding cassette) transporter, BmrA, probed by H/D exchange and solid-state NMR - Jault Jean-Michel - University de Lyon, CNRS | Abstract
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Structural Biology 2018: Mechanism of a bacterial multidrug ABC (ATP-binding cassette) transporter, BmrA, probed by H/D exchange and solid-state NMR - Jault Jean-Michel - University de Lyon, CNRS

Author(s): Jault Jean-Michel

ATP-binding cassette (ABC) transporters can translocate a massive variety of molecules across a membrane by coupling transport with ATP hydrolysis. They are discovered in all dwelling organisms and some individuals of this superfamily are involved in resistance to many unrelated compounds (e.g. antibiotics, anticancer us and antifungal) and consequently confer a multidrug resistance phenotype. Our research focal point on BmrA, a prototypical bacterial multidrug ABC transporter from Bacillus subtilis which is homologous to the human P-glycoprotein concerned in resistance of cancerous cells to therapeutic drugs. Using both H/D exchange and solid-state NMR, we had been capable to probe primary conformational variations between the resting nation (inward-facing conformation) and the ATP-bound nation (outward-facing conformation) of BmrA, both in a solubilized detergent form or reconstituted in lipids. Our results highlight the necessary changes in flexibility and conformation between these two states of the catalytic cycle of BmrA, and the flexibility found in the resting country ought to perchance widen the specificity for drug recognition.
Import of vitamins and export of signalling molecules or noxious compounds are quintessential approaches for life, and selectivity for crossing membrane is generally ruled with the aid of dedicated transporters. The ATP-binding cassette (ABC) is one of the greatest families of transporters involved in these “checkpoints.” They are located in all residing species and use ATP hydrolysis to transport a wide variety of substrates. The dysfunctions of quite a few ABC transporters purpose extreme pathologies, such as adrenoleukodystrophy, hyperinsulinemia hypoglycaemia, or cystic fibrosis. Other medically necessary ABC transporters are accountable for multidrug resistance (MDR) phenotypes. Multidrug transporters are capable of recognizing and expelling many unrelated natural compounds with quite distinctive chemical scaffolds. Thus, although their original feature is to shield healthful cells, the incidence of these transporters in malignant tissues, pathogenic microorganisms, or parasites confers a resistance toward the curative drugs. The archetype of multidrug ABC transporters is the human MDR1 (or ABCB1); it is responsible for the failure of chemotherapeutic treatments in cancerous tissues. In bacteria, the identification of related transporters is distinctly recent, compared with different families of multidrug transporters that use the proton gradient as the strength source. However, developing bodies of evidence guide the implication of these multidrug ABC transporters in antibiotic resistance in many species, jeopardizing a profitable therapy. All ABC transporters share a common architecture, with two transmembrane domains (TMDs) accountable for substrate translocation and two nucleotide-binding domains (NBDs). In most exporters, these 4 domains are both linked into a single polypeptide or characteristic as dimers with one NBD fused to one TMD (homo- or heterodimers). As adverse to the TMDs, the NBDs are exceptionally conserved, with quite a few one of a kind motifs, surprisingly the Walker A and Walker B found in many ATPases and the ABC signature unique to this family. NBD structures have proven that at some point of the catalytic cycle, the two NBDs have interaction transiently to structure a sandwich dimer in a head-to-tail fashion, thereby trapping two ATP molecules at their interface. In this closed conformation, which can be stabilized both by using ATPase-inactive mutations or via vanadate-induced ADP trapping, every composite ATP-binding website is made of elements from one NBD (i.e., Walker A and B motifs), whereas the ABC signature is provided in trans by the 2d NBD. The basic shape of exporters is much less compact than that of importers with two giant intracellular domains (ICDs), ICD1 and ICD2, which protrude from the TMD to have interaction with the NBD.