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Cryo-EM structure of the ABCG2 E211Q mutant bound to ATP and Magnesium (alternative placement of Magnesium into the cryo-EM density)
Structural highlights
FunctionABCG2_HUMAN High-capacity urate exporter functioning in both renal and extrarenal urate excretion. Plays a role in porphyrin homeostasis as it is able to mediates the export of protoporhyrin IX (PPIX) both from mitochondria to cytosol and from cytosol to extracellular space, and cellular export of hemin, and heme. Xenobiotic transporter that may play an important role in the exclusion of xenobiotics from the brain. Appears to play a major role in the multidrug resistance phenotype of several cancer cell lines. Implicated in the efflux of numerous drugs and xenobiotics: mitoxantrone, the photosensitizer pheophorbide, camptothecin, methotrexate, azidothymidine (AZT), and the anthracyclines daunorubicin and doxorubicin.[1] [2] [3] [4] Publication Abstract from PubMedABCG2 is a transporter protein of the ATP-binding-cassette (ABC) family that is expressed in the plasma membrane in cells of various tissues and tissue barriers, including the blood-brain, blood-testis and maternal-fetal barriers(1-4). Powered by ATP, it translocates endogenous substrates, affects the pharmacokinetics of many drugs and protects against a wide array of xenobiotics, including anti-cancer drugs(5-12). Previous studies have revealed the architecture of ABCG2 and the structural basis of its inhibition by small molecules and antibodies(13,14). However, the mechanisms of substrate recognition and ATP-driven transport are unknown. Here we present high-resolution cryo-electron microscopy (cryo-EM) structures of human ABCG2 in a substrate-bound pre-translocation state and an ATP-bound post-translocation state. For both structures, we used a mutant containing a glutamine replacing the catalytic glutamate (ABCG2EQ), which resulted in reduced ATPase and transport rates and facilitated conformational trapping for structural studies. In the substrate-bound state, a single molecule of estrone-3-sulfate (E1S) is bound in a central, hydrophobic and cytoplasm-facing cavity about halfway across the membrane. Only one molecule of E1S can bind in the observed binding mode. In the ATP-bound state, the substrate-binding cavity has collapsed while an external cavity has opened to the extracellular side of the membrane. The ATP-induced conformational changes include rigid-body shifts of the transmembrane domains, pivoting of the nucleotide-binding domains (NBDs), and a change in the relative orientation of the NBD subdomains. Mutagenesis and in vitro characterization of transport and ATPase activities demonstrate the roles of specific residues in substrate recognition, including a leucine residue that forms a 'plug' between the two cavities. Our results show how ABCG2 harnesses the energy of ATP binding to extrude E1S and other substrates, and suggest that the size and binding affinity of compounds are important for distinguishing substrates from inhibitors. Cryo-EM structures of a human ABCG2 mutant trapped in ATP-bound and substrate-bound states.,Manolaridis I, Jackson SM, Taylor NMI, Kowal J, Stahlberg H, Locher KP Nature. 2018 Nov;563(7731):426-430. doi: 10.1038/s41586-018-0680-3. Epub 2018 Nov, 7. PMID:30405239[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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