ABCMdb

ABCB1 p.Phe942Ala

Predicted by SNAP2:	A: D (66%), C: D (53%), D: D (85%), E: D (85%), G: D (75%), H: D (71%), I: D (71%), K: D (85%), L: D (59%), M: N (57%), N: D (66%), P: D (85%), Q: D (71%), R: D (85%), S: D (66%), T: D (75%), V: D (71%), W: D (75%), Y: N (82%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, G: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, Q: D, R: D, S: D, T: D, V: D, W: D, Y: N,

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Publications
[hide] Identification of residues in the drug-binding dom... J Biol Chem. 1999 Dec 10;274(50):35388-92. Loo TW, Clarke DM
Identification of residues in the drug-binding domain of human P-glycoprotein. Analysis of transmembrane segment 11 by cysteine-scanning mutagenesis and inhibition by dibromobimane.
J Biol Chem. 1999 Dec 10;274(50):35388-92., 1999-12-10 [PMID:10585407]

Abstract [show]
The drug-binding domain of the human multidrug resistance P-glycoprotein (P-gp) probably consists of residues from multiple transmembrane (TM) segments. In this study, we tested whether the amino acids in TM11 participate in binding drug substrates. Each residue in TM11 was initially altered by site-directed mutagenesis and assayed for drug-stimulated ATPase activity in the presence of verapamil, vinblastine, or colchicine. Mutants G939V, F942A, T945A, Q946A, A947L, Y953A, A954L, and G955V had altered drug-stimulated ATPase activities. Direct evidence for binding of drug substrate was then determined by cysteine-scanning mutagenesis of the residues in TM11 and inhibition of drug-stimulated ATPase activity by dibromobimane, a thiol-reactive substrate. Dibromobimane inhibited the drug-stimulated ATPase activities of two mutants, F942C and T945C, by more than 75%. These results suggest that residues Phe(942) and Thr(945) in TM11, together with residues previously identified in TM6 (Leu(339) and Ala(342)) and TM12 (Leu(975), Val(982), and Ala(985)) (Loo, T. W., and Clarke, D. M. (1997) J. Biol. Chem. 272, 31945-31948) form part of the drug-binding domain of P-gp.

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No. Sentence Comment
79 Wild-type P-gp had an apparent affinity of 24 ␮M verapamil, while mutants F942A, T945A, Q946A, A947L, and Y953A had decreased apparent affinities of 93, 100, 165, 156, and 110 ␮M, respectively. Login to comment
83 By contrast, mutants A954L and F942A had only 13 and 30%, respectively, of the wild-type activity. Login to comment
100 There were, however, significant decreases in the activity for mutants Q946A (18%), F942A (24%), and F957A (32%). Login to comment
128 TABLE I Drug-stimulated ATPase activity Mutant Drug Verapamil Vinblastine Colchicine Vmax Km Vmax Km Vmax Km % of WTa ␮M % of WT ␮M % of WT mM WT 100 24 100 5.4 100 0.62 I937S 94 22 93 6.1 100 0.69 F938A 106 32 96 5.1 96 0.68 G939V 62 8 45 4.0 165 0.26 I940S 93 32 93 5.6 93 0.65 T941A 100 25 104 5.5 100 0.66 F942A 88 93 30 5.1 24 0.80 S943A 92 26 100 5.2 85 0.62 F944A 93 14 105 5.3 101 0.64 T945A 140 100 165 8.3 56 0.65 Q946A 101 165 57 8.5 18 0.64 A947L 105 156 60 13.0 51 1.87 M948A 103 23 101 5.9 103 0.62 M949A 82 40 96 5.5 61 0.60 Y950A 109 37 119 5.1 99 0.62 F951A 94 31 99 5.2 101 0.64 S952A 108 36 123 5.1 91 0.69 Y953A 205 110 59 8.5 131 0.67 A954L 108 44 13 NDb 8 ND G955V 143 10 104 3.5 220 0.47 C956A 97 24 95 5.3 145 0.63 F957A 126 21 47 4.8 32 1.0 a WT, wild type. b ND, not determined due to low activity. Login to comment
147 DISCUSSION Mutants G939V, F942A, T945A, Q946A, A947L, and Y953A in TM11 had altered apparent affinities for verapamil, vinblastine, or colchicine. Login to comment

[hide] Interaction of digitalis-like compounds with p-gly... Toxicol Sci. 2013 Feb;131(2):502-11. doi: 10.1093/toxsci/kfs307. Epub 2012 Oct 26. Gozalpour E, Wittgen HG, van den Heuvel JJ, Greupink R, Russel FG, Koenderink JB
Interaction of digitalis-like compounds with p-glycoprotein.
Toxicol Sci. 2013 Feb;131(2):502-11. doi: 10.1093/toxsci/kfs307. Epub 2012 Oct 26., [PMID:23104431]

Abstract [show]
Digitalis-like compounds (DLCs), or cardiac glycosides, are produced and sequestered by certain plants and animals as a protective mechanism against herbivores or predators. Currently, the DLCs digoxin and digitoxin are used in the treatment of cardiac congestion and some types of cardiac arrhythmia, despite a very narrow therapeutic index. P-glycoprotein (P-gp; ABCB1) is the only known ATP-dependent efflux transporter that handles digoxin as a substrate. Ten alanine mutants of human P-gp drug-binding amino acids-Leu(65), Ile(306), Phe(336), Ile(340), Phe(343), Phe(728), Phe(942), Thr(945), Leu(975), and Val(982)-were generated and expressed in HEK293 cells with a mammalian baculovirus system. The uptake of [(3)H]-N-methyl-quinidine (NMQ), the P-gp substrate in vesicular transport assays, was determined. The mutations I306A, F343A, F728A, T945A, and L975A abolished NMQ transport activity of P-gp. For the other mutants, the apparent affinities for six DLCs (cymarin, digitoxin, digoxin, peruvoside, proscillaridin A, and strophanthidol) were determined. The affinities of digoxin, proscillaridin A, peruvoside, and cymarin for mutants F336A and I340A were decreased two- to fourfold compared with wild type, whereas that of digitoxin and strophanthidol did not change. In addition, the presence of a hydroxyl group at position 12beta seems to reduce the apparent affinity when the side chain of Phe(336) and Phe(942) is absent. Our results showed that a delta-lactone ring and a sugar moiety at 3beta of the steroid body are favorable for DLC binding to P-gp. Moreover, DLC inhibition is increased by hydroxyl groups at positions 5beta and 19, whereas inhibition is decreased by those at positions 1beta, 11alpha, 12beta, and 16beta. The understanding of the P-gp-DLC interaction improves our insight into DLCs toxicity and might enhance the replacement of digoxin with other DLCs that have less adverse drug effects.

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No. Sentence Comment
46 However, transport activity was preserved in L65A, I306A, I340A, F942A, and V982A. Login to comment
62 Ten different P-gp mutants were produced: L65A, I306A, F336A, I340A, F343A, F728A, F942A, T945A, L975A, and V982A and all mutations were confirmed by sequencing of full-length P-gp cDNA. Login to comment
122 All the indicated amino acids were replaced by alanine to remove the side chain of the residue (L65A, I306A, F336A, I340A, F343A, F728A, F942A, T945A, L975A, and V982A). Login to comment
132 NMQ transport activity of mutants L65A, F336A, I340A, F942A, andV982A as compared with wild-type P-gp ranged from 60 to 150%, whereas NMQ transport activity of I306A, F343A, F728A, T945A, and L975A varied between 8 and 30%. Login to comment
135 In addition, five P-gp mutants (L65A, F336A, I340A, F942A, and V982A), for which NMQ transport activity was at least 50% of wild-type transport, were selected. Login to comment
140 F942A seems to affect the digoxin binding (3.0), although not significantly. Login to comment
180 Fig. 5.ߓ Western blot analysis (A) and NMQ transport activity of wild type and L65A, I306A, F336A, I340A, F343A, F728A, F942A, T945A, L975A, and V982A mutant P-gp (B). Login to comment
202 NMQ transport activity of the second group mutants (L65A, F336A, I340A, F942A, and V982A) was not significantly different from that of the wild-type P-gp (60-150%). Login to comment
208 Table 1 The IC50 Values of DLCs Against Wild-Type and Mutant P-gp-Mediated [3 H]-NMQ Transport P-gp Cymarin Digitoxin Digoxin Peruvoside Proscillaridin A Strophanthidol IC50 (&#b5;M) RIC50 IC50 (&#b5;M) RIC50 IC50 (&#b5;M) RIC50 IC50 (&#b5;M) RIC50 IC50 (&#b5;M) RIC50 IC50 (&#b5;M) RIC50 Wild type 432ߙ&#b1;ߙ90 9ߙ&#b1;ߙ2.1 188ߙ&#b1;ߙ24 214ߙ&#b1;ߙ41 25ߙ&#b1;ߙ3.5 242ߙ&#b1;ߙ61 L65A 800ߙ&#b1;ߙ99 1.9 17ߙ&#b1;ߙ3.4 1.9 217ߙ&#b1;ߙ33 1.2 469ߙ&#b1;ߙ73* 2.2 48ߙ&#b1;ߙ7.2 1.9 186ߙ&#b1;ߙ18 0.8 F336A 979ߙ&#b1;ߙ48 2.3 14ߙ&#b1;ߙ1.9 1.6 524ߙ&#b1;ߙ114 2.8 528ߙ&#b1;ߙ92** 2.5 111ߙ&#b1;ߙ19** 4.4 291ߙ&#b1;ߙ45 1.2 I340A 1181ߙ&#b1;ߙ103** 2.7 19ߙ&#b1;ߙ4.3 2.0 439ߙ&#b1;ߙ138 2.3 527ߙ&#b1;ߙ37** 2.5 79ߙ&#b1;ߙ21* 3.1 156ߙ&#b1;ߙ14 0.6 F942A 821ߙ&#b1;ߙ256 1.9 8ߙ&#b1;ߙ1.0 0.9 558ߙ&#b1;ߙ145 3.0 273ߙ&#b1;ߙ29 1.3 18ߙ&#b1;ߙ1 0.7 187ߙ&#b1;ߙ24 0.8 V982A 620ߙ&#b1;ߙ106 1.4 12ߙ&#b1;ߙ2.1 1.3 345ߙ&#b1;ߙ73 1.8 291ߙ&#b1;ߙ10 1.4 22ߙ&#b1;ߙ3.4 0.9 144ߙ&#b1;ߙ9 0.6 Note. Login to comment
213 Inhibition of NMQ transport by L65A, F942A, and V982A with six DLCs showed that in only one case the mutation caused a significant difference in the IC50 value (ratio of 2.2) of the DLCs compared with wild-type P-gp. Login to comment

[hide] Convallatoxin: a new P-glycoprotein substrate. Eur J Pharmacol. 2014 Dec 5;744:18-27. doi: 10.1016/j.ejphar.2014.09.031. Epub 2014 Sep 28. Gozalpour E, Greupink R, Bilos A, Verweij V, van den Heuvel JJ, Masereeuw R, Russel FG, Koenderink JB
Convallatoxin: a new P-glycoprotein substrate.
Eur J Pharmacol. 2014 Dec 5;744:18-27. doi: 10.1016/j.ejphar.2014.09.031. Epub 2014 Sep 28., [PMID:25264938]

Abstract [show]
Digitalis-like compounds (DLCs), such as digoxin and digitoxin that are derived from digitalis species, are currently used to treat heart failure and atrial fibrillation, but have a narrow therapeutic index. Drug-drug interactions at the transporter level are frequent causes of DLCs toxicity. P-glycoprotein (P-gp, ABCB1) is the primary transporter of digoxin and its inhibitors influence pharmacokinetics and disposition of digoxin in the human body; however, the involvement of P-gp in the disposition of other DLCs is currently unknown. In present study, the transport of fourteen DLCs by human P-gp was studied using membrane vesicles originating from human embryonic kidney (HEK293) cells overexpressing P-gp. DLCs were quantified by liquid chromatography-mass spectrometry (LC-MS). The Lily of the Valley toxin, convallatoxin, was identified as a P-gp substrate (Km: 1.1+/-0.2 mM) in the vesicular assay. Transport of convallatoxin by P-gp was confirmed in rat in vivo, in which co-administration with the P-gp inhibitor elacridar, resulted in increased concentrations in brain and kidney cortex. To address the interaction of convallatoxin with P-gp on a molecular level, the effect of nine alanine mutations was compared with the substrate N-methyl quinidine (NMQ). Phe343 appeared to be more important for transport of NMQ than convallatoxin, while Val982 was particularly relevant for convallatoxin transport. We identified convallatoxin as a new P-gp substrate and recognized Val982 as an important amino acid involved in its transport. These results contribute to a better understanding of the interaction of DLCs with P-gp.

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No. Sentence Comment
56 Nine different P-gp mutants, I306A, F336A, I340A, F343A, F728A, F942A, T945A, L975A, and V982A, were produced and sequencing of full-length P-gp cDNA was used to confirm all mutations (Gozalpour et al., 2013). Login to comment
154 Nine amino acids were replaced by alanine (I306A, F336A, I340A, F343A, F728A, F942A, T945A, L975A, and V982A) and P-gp mutants were expressed in HEK293 cells to produce membrane vesicles. Login to comment
168 The transport activity of F336A, F942A, T945A and L975A for NMQ ranged from 49% to 57%, whereas I340A showed increased activity of 120% and V982A had about the same activity as wild type (Fig. 5B). Login to comment
170 Convallatoxin and NMQ transport activity were not significantly different for I306A, F336A, I340A, F728A, F942A, T945A, and L975A (Fig. 5C), whereas they differed significantly for F343A and V982A (Fig. 5D and E). Login to comment
254 The transport activity of F336A, F942A, T945A, L975A and V982A, were conserved (45-100% of wild type) (Fig. 5B) similar to our previous results (Gozalpour et al., 2013). Login to comment
255 Convallatoxin transport activity of most mutants (I306A, F336A, I340A, F728A, F942A, T945, and L975) was similar to that of NMQ. Login to comment