5/19/2023 0 Comments Abc transporter![]() In this outward-facing (OF) conformation, two ATP molecules are occluded at the NBD dimer interface: one in the catalytically inactive, degenerate site and the other in the active consensus site, poised for hydrolysis ( Figure 1A). Meanwhile, the LTC 4-binding pocket becomes deformed, no longer competent to bind substrate. Upon binding of ATP, the transporter adopts its fully NBD-closed configuration concurrent with opening of the translocation pathway to the outside. Binding of LTC 4 at the center of the membrane, between TMD1 and TMD2, brings the two halves of the transporter closer together. In the absence of ATP, MRP1 adopts an inward-facing (IF) conformation, in which the two NBDs are widely separated and the translocation pathway is open to the cytoplasm. These structures, in accord with decades of functional analysis ( Cole, 2014a) bring about the following understanding of the transport cycle. Structures of bovine MRP1 (bMRP1) have been determined by electron cryo-microscopy (cryo-EM) in three functional states ( Johnson and Chen, 2017 Johnson and Chen, 2018): an apo form in the absence of substrate and ATP, a complex with the native substrate leukotriene C 4 (LTC 4) in the absence of ATP, and a structure of the hydrolysis-deficient E1454Q mutant determined in the presence of both LTC 4 and ATP ( Figure 1A). MRP1 is a single polypeptide comprising three transmembrane domains (TMD0, TMD1, and TMD2) and two cytosolic nucleotide-binding domains (NBD1 and NBD2). MRP1 also transports a number of chemotherapeutic agents, thereby conferring drug resistance in acute myeloblastic and lymphoblastic leukemia, non-small-cell lung cancer, prostate cancer, breast cancer, and neuroblastoma ( Berger et al., 2005 Cole, 2014b Filipits et al., 2005 Haber et al., 2006 Winter et al., 2013 Zalcberg et al., 2000). Native substrates of MRP1 include a variety of antioxidants, pro-inflammatory molecules, and hormones ( Cole and Deeley, 2006 Deeley and Cole, 2006 Deeley et al., 2006 Leslie et al., 2005). Multidrug resistance protein 1 (MRP1) is an ATP-binding cassette (ABC) transporter that harnesses the energy of ATP to extrude substrates from the cytosol to the extracellular space ( Cole, 2014a). The combination of structural and kinetic data illustrates how different conformations of MRP1 are temporally linked and how substrate and ATP alter protein dynamics to achieve active transport. The rate-limiting step of the transport cycle is the dissociation of the nucleotide-binding-domain dimer, while ATP hydrolysis per se does not reset MRP1 to the resting state. Our results show that substrate stimulates ATP hydrolysis by accelerating the IF-to-OF transition. We also determined the structure of bMRP1 under active turnover conditions. Here, we used single-molecule fluorescence spectroscopy to track the conformational changes of bovine MRP1 (bMRP1) in real time. Previously, the structures of MRP1 were determined in an inward-facing (IF) or outward-facing (OF) conformation. Multidrug resistance protein 1 (MRP1) is an ABC exporter that extrudes a variety of chemotherapeutic agents and native substrates. While their structures have been widely reported, the kinetics governing their transport cycles remain largely unexplored. Please see for revised estimates.ATP-binding cassette (ABC) transporters are molecular pumps ubiquitous across all kingdoms of life. We also discuss the impact and limitations of model systems and structure prediction methods in understanding human ABC transporters and discuss current challenges and future research directions.Įxpected final online publication date for the Annual Review of Biophysics, Volume 52 is May 2023. Here we review this recent progress, highlighting the physiological relevance of human ABC transporters and mechanistic insights gleaned from their direct structure determination. As a result, experimentally determined structures of multiple members of each of the five families of ABC transporters in humans are now available. Over the last decade, advances in structural biology have vastly expanded our mechanistic understanding of human ABC transporter function, revealing details of their molecular arrangement, regulation, and interactions, facilitated in large part by advances in cryo-EM that have rendered hitherto inaccessible targets amenable to high-resolution structural analysis. Of these genes, 44 (in five distinct families) encode for membrane transporters, of which several are involved in drug resistance and disease pathways resulting from transporter dysfunction. Humans have 48 ABC genes organized into seven distinct families. ABC transporters are essential for cellular physiology.
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