ABCB1 p.Phe978Cys
| Predicted by SNAP2: | A: D (66%), C: N (57%), D: D (91%), E: D (85%), G: D (80%), H: D (80%), I: N (78%), K: D (85%), L: N (66%), M: N (53%), N: D (75%), P: D (91%), Q: D (71%), R: D (85%), S: N (53%), T: D (71%), V: N (61%), W: D (85%), Y: D (66%), |
| 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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[hide] Transmembrane helix 12 modulates progression of th... Biochemistry. 2009 Jul 7;48(26):6249-58. Crowley E, O'Mara ML, Reynolds C, Tieleman DP, Storm J, Kerr ID, Callaghan R
Transmembrane helix 12 modulates progression of the ATP catalytic cycle in ABCB1.
Biochemistry. 2009 Jul 7;48(26):6249-58., 2009-07-07 [PMID:19456124]
Abstract [show]
Multidrug efflux pumps, such as P-glycoprotein (ABCB1), present major barriers to the success of chemotherapy in a number of clinical settings. Molecular details of the multidrug efflux process by ABCB1 remain elusive, in particular, the interdomain communication associated with bioenergetic coupling. The present investigation has focused on the role of transmembrane helix 12 (TM12) in the multidrug efflux process of ABCB1. Cysteine residues were introduced at various positions within TM12, and their effect on ATPase activity, nucleotide binding, and drug interaction were assessed. Mutation of several residues within TM12 perturbed the maximal ATPase activity of ABCB1, and the underlying cause was a reduction in basal (i.e., drug-free) hydrolysis of the nucleotide. Two of the mutations (L976C and F978C) were found to reduce the binding of [gamma-(32)P]-azido-ATP to ABCB1. In contrast, the A980C mutation within TM12 enhanced the rate of ATP hydrolysis; once again, this was due to modified basal activity. Several residues also caused reductions in the potency of stimulation of ATP hydrolysis by nicardipine and vinblastine, although the effects were independent of changes in drug binding per se. Overall, the results indicate that TM12 plays a key role in the progression of the ATP hydrolytic cycle in ABCB1, even in the absence of the transported substrate.
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No. Sentence Comment
6 Two of the mutations (L976C and F978C) were found to reduce the binding of [γ-32 P]-azido-ATP to ABCB1.
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ABCB1 p.Phe978Cys 19456124:6:32
status: NEW67 This necessitated the centrifugation (100000g for 30 min) of 500 μL Table 1: Mutagenic Oligonucleotide Primers Used To Generate TM12 Mutationsa mutation primer sequence (50 -30 ) diagnostic restriction digest L976C GAGGATGTTCTAtgtGTATTTTCAGCTGTTG -SpeI F978C GTTCTACTAGTATgTTCtGCaGTTGTCTTTGGTG +PstI A980C CTACTAGTATTTTCAtgcGTTGTCTTTGGTGCCATGGCC -PvuII V982C CTAGTATTTTCAGCgGTTtgCTTTGGTGCCATGGCC -PvuII G984C GCTGTTGTCTTTtGTGCtATGGCCGTGG -NcoI M986C GTATTTGGTGCttgtGCtGTGGGGCAAGTC -NcoI V988C GGTGCCATGGCCtgtGGGCAAGTCAGTTC -BstXI G989C CTTTGGTGCCATGGCCGTGtGcCAAGTCAGTTCATTTGC +BstXI Q990C GGCCGTGGGGtgtGTCtcTTCATTTGCTCC +EarI a Primer sequences contain an introduced cysteine residue (bold) and additional silent mutations (lower case), with respect to the coding sequence that generates or removes the indicated restriction site.
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ABCB1 p.Phe978Cys 19456124:67:259
status: NEW118 The most striking alterations were the approximately 5-fold reductions in basal ATPase activity for the L976C (Vmax=26 ( 4 nmol min-1 mg-1 )and F978C (Vmax=27 ( 9 nmol min-1 mg-1 ) mutations compared to the control cysteine-less isoform of ABCB1.
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ABCB1 p.Phe978Cys 19456124:118:144
status: NEW141 L976C (Vmax = 231 ( 80 nmol min-1 mg-1 ), F978C (Vmax = 142 ( 40 nmol min-1 mg-1 ), V988C, G989C, and Q990C all caused statisticallysignificant (p<0.05) reductionsinthe Vmax valuesfor nicardipine-stimulated ATPase activities (Figure 4B).
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ABCB1 p.Phe978Cys 19456124:141:42
status: NEW146 However, the F978C isoform did display an altered nicardipine-ABCB1 interaction; that is, the potency of nicardipine was reduced from 4.1 ( 1.1 to 24.1 ( 2.3 μM. Vinblastine also stimulates the ATPase activity of ABCB1.
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ABCB1 p.Phe978Cys 19456124:146:13
status: NEW149 For example, mutations L976C, F978C, V988C, and Q990C all displayed statistically significant reductions in maximal ATPase activity in the presence of vinblastine compared to the control cysteine-less isoform.
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ABCB1 p.Phe978Cys 19456124:149:30
status: NEW150 However, of these, only the F978C isoform again displayed a reduction in the potency for stimulation of its ATPase activity by vinblastine, although the degree of stimulation remained unaffected.
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ABCB1 p.Phe978Cys 19456124:150:28
status: NEW155 Table 2: Potency and Degree of Drug Stimulation of ATP Hydrolysis by ABCB1a nicardipine vinblastine EC50 (μM) fold stimulation EC50 (μM) fold stimulation Cys-less 4.1 ( 1.1 4.0 ( 0.6 5.91 ( 2.9 2.2 ( 0.2 L976C 5.2 ( 0.2 7.4 ( 1.4 10.0 ( 0.0 3.5 ( 0.6 F978C 24.1 ( 2.3b 9.5 ( 1.4 42.9 ( 4.3b 2.3 ( 0.5 A980C 3.4 ( 0.3 5.1 ( 0.9 12.3 ( 1.8 3.2 ( 0.8 V982C 5.8 ( 0.9 4.2 ( 0.5 2.0 ( 0.7 1.8 ( 0.2 G984C 37.6 ( 11.2b 16.2 ( 6.6b 6.7 ( 1.7 6.2 ( 2.3 M986C 9.2 ( 0.8 4.7 ( 1.1 15.0 ( 2.0b 2.8 ( 0.7 V988C 3.9 ( 0.6 3.1 ( 0.1 7.3 ( 2.3 1.9 ( 0.2 G989C 13.6 ( 1.5 5.1 ( 1.6 4.9 ( 0.9 2.4 ( 0.3 Q990C 6.9 ( 1.1 3.7 ( 1.0 NDc NDc S992C 4.9 ( 0.5 4.2 ( 0.6 7.1 ( 2.6 2.3 ( 0.4 F994C 1.7 ( 0.4 3.2 ( 0.8 5.9 ( 2.5 1.6 ( 0.3 a ATPase activity was plotted as a function of the drug concentration and potency (EC50) and degree of stimulation obtained by nonlinear regression of the dose-response relationship equation.
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ABCB1 p.Phe978Cys 19456124:155:263
status: NEW172 Figure 5A presents a representative autoradiogram of [γ-32 P]-azido-ATP binding to the mutants L976C, F978C, A980C, V988C, G989C, and Q990C.
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ABCB1 p.Phe978Cys 19456124:172:108
status: NEW174 The results indicate that at a concentration of 10 μM [γ-32 P]-azido-ATP there was a discernible difference between the binding of the ATP analogue to L976C, F978C, and A980C.
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ABCB1 p.Phe978Cys 19456124:174:170
status: NEW175 Mutant isoforms L976C and F978C displayed a 4and 15-fold decrease in binding, whereas A980C showed a 1.8-fold increase in binding at the concentration of [γ-32 P]-azido-ATP used.
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ABCB1 p.Phe978Cys 19456124:175:26
status: NEW179 Figure 5C shows the densitometric analysis of the dose-response curve for the cysteine-less, A980C, L976C, and F978C isoforms.
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ABCB1 p.Phe978Cys 19456124:179:111
status: NEW181 In contrast, the mutant isoforms L976C (Bmax = 0.24, KD = 17 μM) and F978C (Bmax = 0.19, KD =17 μM) displayed 4-5-fold reductions in the amount of [γ-32 P]-azido-ATP binding compared to the cysteine-less control.
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ABCB1 p.Phe978Cys 19456124:181:75
status: NEW182 Therefore, the decrease in basal and drug-stimulated ATPase activity observed for the L976C and F978C isoforms can be explained at least in part by impaired ATP binding at the NBDs.
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ABCB1 p.Phe978Cys 19456124:182:96
status: NEW187 To investigate whether such differences are a reflection of a physical asymmetry between the helices and their surroundings, we attempted to rationalize three of the functionally perturbed TM12 single cysteine mutants (i.e., F978C, A980C, and V988C) byreference toamolecularmodel ofABCB1.
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ABCB1 p.Phe978Cys 19456124:187:225
status: NEW193 (C) Data obtained for the cysteine-less, L976C, F978C, and A980C isoforms were analyzed by densitometry, and the amount bound was plotted as a function of the [γ-32 P]-azido-ATP concentration.
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ABCB1 p.Phe978Cys 19456124:193:48
status: NEW203 The F978C mutation, located near the extracellular protein-lipid interface in the membrane-embedded region of TM12, is part of a conserved sequence motif present in TM12 and TM6.
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ABCB1 p.Phe978Cys 19456124:203:4
status: NEW207 However, unlike the TM12 F978C mutation, the TM6 F335C mutation does not cause a significant reduction in ATPase activity (15).
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ABCB1 p.Phe978Cys 19456124:207:25
status: NEW208 In TM12, mutation to the smaller 978C increases the distance between F978C and F72, preventing hydrophobic interactions (Figure 6D) and decreasing the number of TM12-TM1 contact points.
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ABCB1 p.Phe978Cys 19456124:208:69
status: NEW210 Interestingly, the modeled mutation also alters the orientation of the F978C side chain, resulting in the complete exposure of the cysteine side chain into a pore below L975, which has been implicated in dibromobimane binding (47).
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ABCB1 p.Phe978Cys 19456124:210:71
status: NEW220 The most dramatic effects in TM12 were observed in residues at the extracellular Table 3: Nucleotide Binding to ABCB1a ABCB1 isoform [32 P]-N3-ATP [32 P]-N3-ATP+ 1 mM ATP [32 P]-N3-ATP+ 1 mM ADP Cys-less 1.00 0.21 ( 0.05 0.23 ( 0.06 L976C 0.21 ( 0.05 0.10 ( 0.02 0.05 ( 0.03 F978C 0.07 ( 0.01 ND ND A980C 1.81 ( 0.71 0.45 ( 0.10 0.15 ( 0.08 V988C 0.53 ( 0.20 ND ND G989C 0.83 ( 0.04 0.10 ( 0.05 0.13 ( 0.06 Q990C 1.05 ( 0.30 0.19 ( 0.11 0.01 ( 0.01 a The ABCB1 isoforms were incubated with 10 μM [γ32 P]-azido-ATP in the presence or absence of excess unlabeled nucleotides (1 mM).
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ABCB1 p.Phe978Cys 19456124:220:275
status: NEW231 (D) Mutation to F978C (CPK) prevents hydrogen bonding to F72.
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ABCB1 p.Phe978Cys 19456124:231:16
status: NEW232 (L976C and F978C) and intracellular (V988C and Q990C) ends of the helix.
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ABCB1 p.Phe978Cys 19456124:232:11
status: NEW234 In contrast, the reduced basal activity observed with mutants L976C and F978C appeared to be a consequence of reduced nucleotide binding.
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ABCB1 p.Phe978Cys 19456124:234:72
status: NEW[hide] Inhibition of oxidative cross-linking between engi... J Biol Chem. 1996 Nov 1;271(44):27482-7. Loo TW, Clarke DM
Inhibition of oxidative cross-linking between engineered cysteine residues at positions 332 in predicted transmembrane segments (TM) 6 and 975 in predicted TM12 of human P-glycoprotein by drug substrates.
J Biol Chem. 1996 Nov 1;271(44):27482-7., 1996-11-01 [PMID:8910331]
Abstract [show]
Each homologous half of P-glycoprotein consists of a transmembrane domain with six potential transmembrane segments and an ATP-binding domain. Labeling studies with photoactive drug analogs show that labeling occurs within or close to predicted transmembrane segments (TM) 6 (residues 331-351) and TM12 (residues 974-994). To test if these segments are in near-proximity we generated 42 different P-glycoprotein mutants in which we re-introduced a pair of cysteine residues into a Cys-less P-glycoprotein, one within TM6 (residues 332-338) and one within TM12 (residues 975-980) and assayed for cross-linking between the cysteines. All the mutants retained verapamil-stimulated ATPase activity. We found that only the mutant containing Cys-332 and Cys-975 was cross-linked in the presence of oxidant as judged by its decreased mobility on SDS gels. Similar results were obtained when the same mutations were introduced into Cys-less NH2-terminal and COOH-terminal half-molecules of P-glycoprotein followed by coexpression and treatment with oxidant. Cross-linking between Cys-332 and Cys-975, however, was inhibited by verapamil or vinblastine but not by colchicine. These results suggest that residues Cys-332 and Cys-975, which occupy equivalent positions when TM6 and TM12 are aligned, are close to each other in the tertiary structure of P-glycoprotein.
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No. Sentence Comment
66 Accordingly, site-directed mutagenesis was used to change the codon for each residue surrounding Phe-335 and Phe-978 to cysteine (Fig. 1B).
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ABCB1 p.Phe978Cys 8910331:66:109
status: NEW156 A, membranes prepared from cells transfected with vector alone (control) or cotransfected with cDNA for mutant L332C in the Cys-less NH2-terminal half-molecule A52 and the cDNA for mutant L975C in the Cys-less COOH-terminal half-molecule A52 or with cDNA for mutant F335C in the NH2-terminal half-molecule A52 and the cDNA for mutant F978C in the COOH-terminal half-molecule A52 were treated with oxidant for various intervals and at different temperatures.
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ABCB1 p.Phe978Cys 8910331:156:334
status: NEW[hide] Identification of residues in the drug-binding sit... J Biol Chem. 1997 Dec 19;272(51):31945-8. Loo TW, Clarke DM
Identification of residues in the drug-binding site of human P-glycoprotein using a thiol-reactive substrate.
J Biol Chem. 1997 Dec 19;272(51):31945-8., 1997-12-19 [PMID:9405384]
Abstract [show]
We identified a thiol-reactive compound, dibromobimane (dBBn), that was a potent stimulator (8.2-fold) of the ATPase activity of Cys-less P-glycoprotein. We then used this compound together with cysteine-scanning mutagenesis to identify residues in transmembrane segment (TM) 6 and TM12 that are important for function. TM6 and TM12 lie close to each other in the tertiary structure and are postulated to be important for drug-protein interactions. The majority of P-glycoprotein mutants containing a single cysteine residue retained substantial amounts of drug-stimulated ATPase activity and were not inhibited by dBBn. The ATPase activities of mutants L339C, A342C, L975C, V982C, and A985C, however, were markedly inhibited (>60%) by dBBn. The drug substrates verapamil, vinblastine, and colchicine protected these mutants against inhibition by dBBn, suggesting that these residues are important for interaction of substrates with P-glycoprotein. We previously showed that residues Leu339, Ala342, Leu975, Val982, and Ala985 lie along the point of contact between helices TM6 and TM12, when both are aligned in a left-handed coiled coil (Loo, T. W., and Clarke, D. M. (1997) J. Biol. Chem. 272, 20986-20989). Taken together, these results suggest that the interface between TM6 and TM12 likely forms part of the potential drug-binding pocket in P-glycoprotein.
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No. Sentence Comment
81 One mutant, F335C (TM6) showed enhanced activity (280%), whereas the equivalent residue in TM12 (F978C) showed decreased activity (31%).
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ABCB1 p.Phe978Cys 9405384:81:97
status: NEW[hide] Multiple transport-active binding sites are availa... PLoS One. 2013 Dec 5;8(12):e82463. doi: 10.1371/journal.pone.0082463. eCollection 2013. Chufan EE, Kapoor K, Sim HM, Singh S, Talele TT, Durell SR, Ambudkar SV
Multiple transport-active binding sites are available for a single substrate on human P-glycoprotein (ABCB1).
PLoS One. 2013 Dec 5;8(12):e82463. doi: 10.1371/journal.pone.0082463. eCollection 2013., [PMID:24349290]
Abstract [show]
P-glycoprotein (Pgp, ABCB1) is an ATP-Binding Cassette (ABC) transporter that is associated with the development of multidrug resistance in cancer cells. Pgp transports a variety of chemically dissimilar amphipathic compounds using the energy from ATP hydrolysis. In the present study, to elucidate the binding sites on Pgp for substrates and modulators, we employed site-directed mutagenesis, cell- and membrane-based assays, molecular modeling and docking. We generated single, double and triple mutants with substitutions of the Y307, F343, Q725, F728, F978 and V982 residues at the proposed drug-binding site with cys in a cysless Pgp, and expressed them in insect and mammalian cells using a baculovirus expression system. All the mutant proteins were expressed at the cell surface to the same extent as the cysless wild-type Pgp. With substitution of three residues of the pocket (Y307, Q725 and V982) with cysteine in a cysless Pgp, QZ59S-SSS, cyclosporine A, tariquidar, valinomycin and FSBA lose the ability to inhibit the labeling of Pgp with a transport substrate, [(125)I]-Iodoarylazidoprazosin, indicating these drugs cannot bind at their primary binding sites. However, the drugs can modulate the ATP hydrolysis of the mutant Pgps, demonstrating that they bind at secondary sites. In addition, the transport of six fluorescent substrates in HeLa cells expressing triple mutant (Y307C/Q725C/V982C) Pgp is also not significantly altered, showing that substrates bound at secondary sites are still transported. The homology modeling of human Pgp and substrate and modulator docking studies support the biochemical and transport data. In aggregate, our results demonstrate that a large flexible pocket in the Pgp transmembrane domains is able to bind chemically diverse compounds. When residues of the primary drug-binding site are mutated, substrates and modulators bind to secondary sites on the transporter and more than one transport-active binding site is available for each substrate.
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No. Sentence Comment
55 For biochemical studies, crude membranes were prepared from High-Five insect cells infected with baculovirus coding for cysless WT, single mutants Y307C, F343C, Q725C, F728C, F978C, V982C, double mutants Y307C/V982C, F343C/V982C, Q725C/V982C, F728C/V982C, and a triple mutant Y307C/Q725C/V982C.
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ABCB1 p.Phe978Cys 24349290:55:175
status: NEW69 One mutant, F978C, behaves in a manner similar to that of cysless WT Pgp, with only a change in the binding affinity for CsA, IC50 = 0.54 &#b5;M, compared to 0.05 &#b5;M for cysless WT Pgp (Table 1).
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ABCB1 p.Phe978Cys 24349290:69:12
status: NEW71 Similarly, tariquidar inhibits IAAP labeling of F978C to the Figure 1.
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ABCB1 p.Phe978Cys 24349290:71:48
status: NEW82 However a majority of the mutants show low basal activity; F728C/V982C shows the lowest (4 &#b1;1.6 nmol Pi/min/mg protein) while V982C and F978C shows fairly low activity (11 &#b1; 2.2 and 13 &#b1; 0.6, respectively).
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ABCB1 p.Phe978Cys 24349290:82:140
status: NEW90 Mutation(s) CsA Tariquidar Max Inhibition (%) IC50 (&#b5;M) Max Inhibition (%) IC50 (&#b5;M) Cysless WT 86 &#b1; 3 0.05 &#b1; 0.01 97 &#b1; 4 0.14 &#b1; 0.03 Q725C 24 &#b1; 4 -- 37 -- Q725C/V982C 11 -- 22 -- Y307C 35 &#b1; 2 -- ND -- Y307C/V982C 46 -- ND -- F728C 48 -- 40 -- F728C/V982C 49 -- ND -- V982C 56 0.40 64 0.70 Y307C/Q725C/ V982C 12 -- 23 -- F978C 86 0.54 73 3.6 Mean values with standard errors are reported when more than two experiments were carried out; otherwise only average values are reported.
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ABCB1 p.Phe978Cys 24349290:90:353
status: NEW175 Mutation(s) Cell surface expression Transport function CalAM BD-PRA NBD-CsA Rh123 Dauno BD-PAC Y307C 100 90-100 80-90 90-100 90-100 90-100 90-100 Q725C 100 90-100 90-100 90-100 90-100 90-100 90-100 F728C 100 90-100 80-90 90-100 90-100 90-100 90-100 V982C 100 90-100 80-100 <10 90-100 90-100 90-100 F343C 50-60 90-100 80-100 90-100 90-100 90-100 90-100 F978C 100 90-100 90-100 90-100 90-100 90-100 90-100 Y307C/ V982C 100 90-100 50-60 50-60 90-100 90-100 90-100 Q725C/ V982C 100 90-100 80-90 <20 90-100 90-100 90-100 F728C/ V982C 30-40 55-65 30-40 <20 70-80 50-60 90-100 F343C/ V982C 70-80 90-100 80-90 <20 90-100 90-100 90-100 Y307/ Q725C/ V982C 100 90-100 30-40 50-60 70-80 60-70 90-100 For cell surface expression, the cells were incubated with MRK-16 antibody for 30 min followed by FITC-labeled anti-mouse secondary antibody for 30 min.
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ABCB1 p.Phe978Cys 24349290:175:352
status: NEW