ABCMdb

ABCB1 p.Gln132Ala

Predicted by SNAP2:	A: D (85%), C: D (80%), D: D (91%), E: D (91%), F: D (91%), G: D (85%), H: D (85%), I: D (91%), K: D (95%), L: D (91%), M: D (85%), N: D (91%), P: D (95%), R: D (91%), S: D (80%), T: D (91%), V: D (91%), W: D (91%), Y: D (85%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, G: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, R: D, S: D, T: D, V: D, W: D, Y: D,

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[hide] Molecular dissection of dual pseudosymmetric solut... Mol Pharmacol. 2011 Mar;79(3):443-52. Epub 2010 Dec 21. Parveen Z, Stockner T, Bentele C, Pferschy S, Kraupp M, Freissmuth M, Ecker GF, Chiba P
Molecular dissection of dual pseudosymmetric solute translocation pathways in human P-glycoprotein.
Mol Pharmacol. 2011 Mar;79(3):443-52. Epub 2010 Dec 21., [PMID:21177413]

Abstract [show]
The human multispecific drug efflux transporter P-glycoprotein (P-gp) causes drug resistance and modulates the pharmacological profile of systemically administered medicines. It has arisen from a homodimeric ancestor by gene duplication. Crystal structures of mouse MDR1A indicate that P-gp shares the overall architecture with two homodimeric bacterial exporters, Sav1866 and MsbA, which have complete rotational symmetry. For ATP-binding cassette transporters, nucleotide binding occurs in two symmetric positions in the motor domains. Based on the homology with entirely symmetric half-transporters, the present study addressed the key question: can biochemical evidence for the existence of dual drug translocation pathways in the transmembrane domains of P-gp be found? P-gp was photolabeled with propafenone analogs, purified, and digested proteolytically, and peptide fragments were identified by high-resolution mass spectrometry. Labeling was assigned to two regions in the protein by projecting data into homology models. Subsequently, symmetric residue pairs in the putative translocation pathways were identified and replaced by site-directed mutagenesis. Transport assays corroborated the existence of two pseudosymmetric translocation pathways. Although rhodamine123 has a preference to take one path, verapamil, propafenones, and vinblastine preferentially use the other. Two major findings ensued from this study: the existence of two solute translocation pathways in P-gp as a reflection of evolutionary origin from a homodimeric ancestor and selective but not exclusive use of one of these pathways by different P-gp solutes. The pseudosymmetric behavior reconciles earlier kinetic and thermodynamic data, suggesting an alternative concept of drug transport by P-gp that will aid in understanding the off-target quantitative structure activity relationships of P-gp interacting drugs.

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No. Sentence Comment
52 Site-directed mutagenesis was performed at positions 132 and 773 of hexahistidine-tagged human P-gp cloned into the entry vector pENTR4-MDR1-His6 to generate the Q132A, Q132R, Q773A, Q773R, and the Q132A/Q773A mutants using the following forward and reverse primers: Q132A: forward, 5Ј-CTG CTT ACA TTG CGG TTT CAT TTT GG-3Ј; reverse, 5Ј-CCA AAA TGA AAC CGC AAT GTA AGC AG-3Ј; Q132R: forward, 5Ј-GCT GCT TAC ATT CGT GTT TCA TTT TG-3Ј; reverse, 5Ј-CAA AAT GAA ACA CGA ATG TAA GCA GC-3Ј; Q773A: forward, 5Ј-CAT TTT TCC TTG CGG GTT TCA CAT TTG GC-3Ј; reverse, 5Ј-GCC AAA TGT GAA ACC CGC AAG GAA AAA TG-3Ј; Q773R: forward, 5Ј-CAT TTT TCC TTC GAG GTT TCA CAT TTG-3Ј; reverse, 5Ј-CAT TTT TCC TTC GAG GTT TCA CAT TTG-3Ј. Login to comment
231 Mutants Q132A (yellow) and Q773A (magenta) lie close to the stippled black line and therefore show transport rates that are comparable with wild-type. Login to comment
267 Indistinguishable IC50 values were found for either compound in the Q132A, the Q773A, and the Q132A/Q773A mutants. Login to comment
299 Mutation IC50 Verapamil Vinblastine GPV31 GPV366 ␮M Wild-type P-gp 0.43 Ϯ 0.10 2.68 Ϯ 0.93 0.11 Ϯ 0.06 2.60 Ϯ 0.69 Q132A 0.30 Ϯ 0.07 2.58 Ϯ 0.31 0.10 Ϯ 0.03 2.57 Ϯ 0.69 Q773A 0.42 Ϯ 0.15 2.80 Ϯ 0.12 0.11 Ϯ 0.05 2.40 Ϯ 1.47 Q132A/Q773A 0.44 Ϯ 0.16 2.24 Ϯ 0.43 0.12 Ϯ 0.01 2.87 Ϯ 0.63 Q132R 1.24 Ϯ 0.13* 9.19 Ϯ 1.20* 0.71 Ϯ 0.46* 2.64 Ϯ 0.59 Q773R 0.14 Ϯ 0.04* 0.45 Ϯ 0.16* 0.02 Ϯ 0.01* 2.09 Ϯ 0.90 * P Ͻ 0.05, significantly different from wild-type values. Login to comment

[hide] The Q loops of the human multidrug resistance tran... FASEB J. 2014 Oct;28(10):4335-46. doi: 10.1096/fj.13-245639. Epub 2014 Jul 11. Zolnerciks JK, Akkaya BG, Snippe M, Chiba P, Seelig A, Linton KJ
The Q loops of the human multidrug resistance transporter ABCB1 are necessary to couple drug binding to the ATP catalytic cycle.
FASEB J. 2014 Oct;28(10):4335-46. doi: 10.1096/fj.13-245639. Epub 2014 Jul 11., [PMID:25016028]

Abstract [show]
For a primary active pump, such as the human ATP-binding-cassette (ABC) transporter ABCB1, coupling of drug-binding by the two transmembrane domains (TMDs) to the ATP catalytic cycle of the two nucleotide-binding domains (NBDs) is fundamental to the transport mechanism, but is poorly understood at the biochemical level. Structure data suggest that signals are transduced through intracellular loops of the TMDs that slot into grooves on the NBDs. At the base of these grooves is the Q loop. We therefore mutated the eponymous glutamine in one or both NBD Q loops and measured the effect on conformation and function by using a conformation-sensitive antibody (UIC2) and a fluorescent drug (Bodipy-verapamil), respectively. We showed that the double mutant is trapped in the inward-open state, which binds the drug, but cannot couple to the ATPase cycle. Our data also describe marked redundancy within the transport mechanism, because single-Q-loop mutants are functional for Bodipy-verapamil transport. This result allowed us to elucidate transduction pathways from twin drug-binding cavities to the Q loops using point mutations to favor one cavity over the other. Together, the data show that the Q loop is the central flexion point where the aspect of the drug-binding cavities is coupled to the ATP catalytic cycle.

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74 Plasmids Mutations were introduced into a plasmid encoding human ABCB1 with a C-terminal hexahistidine tag (pCIneo-wtABCB1-6His; ref. 25) by site-directed mutagenesis (QuikChange XL; Stratagene, La Jolla, CA, USA) using the following oligonucleotides: Q132A, 5=-GGTTGCTGCTTACATCGCGGTTTCATTTTGGTGC- 3=; Q132R, 5=-GGTTGCTGCTTACATTCGAGTTTCATTTTG- GTGC-3=; Q475A, 5=-GGGAAATCATTGGTGTGGTGAGTGCT- GAGCCTGTATTGTTTGCCACCACG-3=; Q773A, 5=-GGAATTA- TTTCTTTTATTACATTTTTCCTTGCGGGTTTCACATTTG- GCAAAGCTGG-3=; Q773R, 5=-GGAATTATTTCTTTTATTA- CATTTTTCCTTCGAGGTTTCACATTTGGCAAAGCTGG-3=; Q1118A, 5=-GGGCATCGTGTCCGCGGAACCCATCCTGTTTG-3=; E556Q, 5=-CCCCAAGATCCTCCTGCTTGATCAGGCCACGT- CAGCCTTGG-3=; and E1201Q, 5=-CAGCCTCATATTTTGCTTCT- TGATCAGGCCACGTCAGCTCTGGATAC-3=. Login to comment