ABCMdb

ABCB1 p.Ile1050Cys

Predicted by SNAP2:	A: N (87%), C: N (78%), D: D (53%), E: N (53%), F: N (78%), G: N (53%), H: N (78%), K: N (66%), L: N (97%), M: N (93%), N: N (72%), P: N (57%), Q: N (82%), R: N (66%), S: N (72%), T: N (82%), V: N (97%), W: N (57%), Y: N (61%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, G: D, H: D, K: D, L: N, M: N, N: D, P: D, Q: D, R: D, S: D, T: D, V: N, W: D, Y: D,

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[hide] The ATPase activity of the P-glycoprotein drug pum... J Biol Chem. 2012 Aug 3;287(32):26806-16. doi: 10.1074/jbc.M112.376202. Epub 2012 Jun 14. Loo TW, Bartlett MC, Detty MR, Clarke DM
The ATPase activity of the P-glycoprotein drug pump is highly activated when the N-terminal and central regions of the nucleotide-binding domains are linked closely together.
J Biol Chem. 2012 Aug 3;287(32):26806-16. doi: 10.1074/jbc.M112.376202. Epub 2012 Jun 14., [PMID:22700974]

Abstract [show]
The P-glycoprotein (P-gp, ABCB1) drug pump protects us from toxic compounds and confers multidrug resistance. Each of the homologous halves of P-gp is composed of a transmembrane domain (TMD) with 6 TM segments followed by a nucleotide-binding domain (NBD). The predicted drug- and ATP-binding sites reside at the interface between the TMDs and NBDs, respectively. Crystal structures and EM projection images suggest that the two halves of P-gp are separated by a central cavity that closes upon binding of nucleotide. Binding of drug substrates may induce further structural rearrangements because they stimulate ATPase activity. Here, we used disulfide cross-linking with short (8 A) or long (22 A) cross-linkers to identify domain-domain interactions that activate ATPase activity. It was found that cross-linking of cysteines that lie close to the LSGGQ (P517C) and Walker A (I1050C) sites of NBD1 and NBD2, respectively, as well as the cytoplasmic extensions of TM segments 3 (D177C or L175C) and 9 (N820C) with a short cross-linker activated ATPase activity over 10-fold. A pyrylium compound that inhibits ATPase activity blocked cross-linking at these sites. Cross-linking between the NBDs was not inhibited by tariquidar, a drug transport inhibitor that stimulates P-gp ATPase activity but is not transported. Cross-linking between extracellular cysteines (T333C/L975C) predicted to lock P-gp into a conformation that prevents close NBD association inhibited ATPase activity. The results suggest that trapping P-gp in a conformation in which the NBDs are closely associated likely mimics the structural rearrangements caused by binding of drug substrates that stimulate ATPase activity.

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No. Sentence Comment
10 It was found that cross-linking of cysteines that lie close to the LSGGQ (P517C) and Walker A (I1050C) sites of NBD1 and NBD2, respectively, as well as the cytoplasmic extensions of TM segments 3 (D177C or L175C) and 9 (N820C) with a short cross-linker activated ATPase activity over 10-fold. Login to comment
93 To address whether trapping the NBDs in close proximity (closed conformation) would activate or inhibit ATPase activity, cysteines were introduced at locations in the central part of NBD1 (P517C) and the N-terminal region of NBD2 (I1050C) of Cys-less P-gp predicted to be outside the catalytic sites but close to the LSGGQ (residues 531-535) and Walker A sites (residues 1070-1077) of NBD1 and NBD2, respectively. Login to comment
95 In the open conformation P517C and I1050C are predicted to be far apart (22.9 Å; measured from the ␣ carbons) but close (7.8 Å) in the closed conformation. Login to comment
96 The P517C/I1050C mutant was expressed in HEK 293 cells. Login to comment
106 The location of residues that were mutated to cysteine to test for the effect of cross-linking between NBD1 and NBD2 (P517C/I1050C), NBD1 and TMD2 (L443C/S909C), ICL1 and ICL3 (D177C/N820C), TM segments 2 and 11 (C137/A935C) or 6 and 12 (T333C/L975C) are shown. Login to comment
107 Linkage of the NBDs Activates P-gp ATPase Activity 26808 JOURNAL OF BIOLOGICAL CHEMISTRY VOLUME 287•NUMBER 32•AUGUST 3, activity mutant P517C/I1050C was highly activated (11.5-fold) by verapamil and exhibited about 80% (1.5 ϩ 0.2 ␮mol Pi/min/mg P-gp) of the verapamil-stimulated ATPase activity of Cys-less P-gp (1.9 ϩ 0.3 ␮mol Pi/min/mg P-gp). Login to comment
108 Cross-linking of P517C/I1050C with M4M increased its basal ATPase activity (14-fold higher than the basal ATPase activity of untreated P-gp) (Fig. 2B). Login to comment
110 The enhanced activity of M4M cross-linked P517C/I1050C was not due to carry over of M4M during purification because M4M had little effect on Cys-less P-gp ATPase activity (Fig. 2B). Login to comment
111 Reduction of M4M cross-linked P517C/I1050C with dithiothreitol decreased its activity back to basal levels (Fig. 2B). Login to comment
112 The large increase in basal ATPase activity observed when mutant P517C/I1050C was cross-linked with the short M4M cross-linker appeared to be caused by trapping of the NBDs in close proximity rather than nonspecific cross-linking effects because treatment with the long M17M cross-linker caused a much smaller increase (about 2-fold) in basal ATPase activity (Fig. 2B). Login to comment
114 The cross-linking results observed with mutant P517C/ I1050C suggest that covalently linking NBD1 and NBD2 in close proximity with M4M mimics activation of ATPase activity with compounds that highly activate P-gp ATPase activity. Login to comment
120 Membranes prepared from cells expressing mutant D177C/ N820C were treated with M4M and M17M. Login to comment
123 A, membranes prepared from HEK 293 cells expressing the NBD1/ NBD2 mutant P517C/I1050C were treated without (Control) or with cross-linkers M4M or M17M. Login to comment
125 The positions of the cross-linked (X-link) and mature (170 kDa) P-gps are indicated. B, membranes expressing mutant P517C/I1050C or Cys-less P-gp were treated with or without (None) cross-linker and histidine-tagged P-gp isolated by nickel-chelate chromatography. Login to comment
136 It was found that the effect of cross-linking on ATPase of mutant D177C/N820C (Fig. 3C) was very similar to those observed for mutant P517C/I1050C (Fig. 2B). Login to comment
158 In previous studies we showed that mutants C137/A935C (39) and L443C/ S909C (27) had verapamil-stimulated ATPase activities similar to Cys-less P-gp. Login to comment
163 These results indicate that stimulation of ATPase activity observed in M4M cross-linked mutants P517C/I1050C (Fig. 2B), D177C/N820C, or L175C/N820C (Fig. 3C) was likely a specific effect of trapping the protein in the closed conformation. Login to comment
194 Mutants that showed activation of ATPase after cross-linking with M4M (P517C/I1050C and D177C/N820C) were tested for inhibition of cross-linking. Login to comment
225 C, cells expressing mutant T333C/L975C were pretreated with 0.1 mM P10, 0.1 mM P12, 0.03 mM tariquidar (Tar), or no compound (None) and then incubated in the absence (-) or presence (ϩ) of 0.5 mM BMOE. Samples were subjected to immunoblot analysis. Login to comment
226 D, membranes prepared from cells expressing mutant P517C/I1050C were pretreated without (None) or with 0.03 mM tariquidar (Tar) followed by incubation in the absence (-) or presence (ϩ) of 0.05 mM M4M cross-linker. Samples were then subjected to immunoblot analysis. Login to comment
232 An explanation for the increased activity is that P517C and I1050C are located at the N-terminal end and central segments of the NBDs close to the LSGGQ and Walker A sites of NBD1 and NBD2, respectively. Login to comment
233 Cross-linking P517C/I1050C (or D177C/ N820C) with M4M would hold the Walker A and LSGGQ sites in close proximity (Fig. 7A) to increase the probability of generating the ATP-bound sandwich conformation and therefore increase the basal ATPase activity. Login to comment
236 The observation that cross-linked mutants P517C/I1050C, D177C/N820C, and L175C/N820C showed high levels of ATPase activity indicates that the protein does not have to adopt an inward-facing conformation with separation of the NBDs for ATP hydrolysis to continue after the first two hydrolysis steps. Login to comment
264 We predict that covalent attachment of thiol-reactive drug substrates to cysteines in the TMDs (or M4M cross-linking of mutants P517C/I1050C, D177C/N820C, or L175C/N820C) traps P-gp in states IV-VI (Fig. 8) that show a high rate of ATP hydrolysis. Login to comment
91 To address whether trapping the NBDs in close proximity (closed conformation) would activate or inhibit ATPase activity, cysteines were introduced at locations in the central part of NBD1 (P517C) and the N-terminal region of NBD2 (I1050C) of Cys-less P-gp predicted to be outside the catalytic sites but close to the LSGGQ (residues 531-535) and Walker A sites (residues 1070-1077) of NBD1 and NBD2, respectively. Login to comment
94 The P517C/I1050C mutant was expressed in HEK 293 cells. Login to comment
104 The location of residues that were mutated to cysteine to test for the effect of cross-linking between NBD1 and NBD2 (P517C/I1050C), NBD1 and TMD2 (L443C/S909C), ICL1 and ICL3 (D177C/N820C), TM segments 2 and 11 (C137/A935C) or 6 and 12 (T333C/L975C) are shown. Login to comment
105 Linkage of the NBDs Activates P-gp ATPase Activity 26808 activity mutant P517C/I1050C was highly activated (11.5-fold) by verapamil and exhibited about 80% (1.5 af9; 0.2 òe;mol Pi/min/mg P-gp) of the verapamil-stimulated ATPase activity of Cys-less P-gp (1.9 af9; 0.3 òe;mol Pi/min/mg P-gp). Login to comment
109 Reduction of M4M cross-linked P517C/I1050C with dithiothreitol decreased its activity back to basal levels (Fig. 2B). Login to comment
122 The positions of the cross-linked (X-link) and mature (170 kDa) P-gps are indicated. B, membranes expressing mutant P517C/I1050C or Cys-less P-gp were treated with or without (None) cross-linker and histidine-tagged P-gp isolated by nickel-chelate chromatography. Login to comment
133 It was found that the effect of cross-linking on ATPase of mutant D177C/N820C (Fig. 3C) was very similar to those observed for mutant P517C/I1050C (Fig. 2B). Login to comment
189 Mutants that showed activation of ATPase after cross-linking with M4M (P517C/I1050C and D177C/N820C) were tested for inhibition of cross-linking. Login to comment
219 D, membranes prepared from cells expressing mutant P517C/I1050C were pretreated without (None) or with 0.03 mM tariquidar (Tar) followed by incubation in the absence (afa;) or presence (af9;) of 0.05 mM M4M cross-linker. Samples were then subjected to immunoblot analysis. Login to comment
229 The observation that cross-linked mutants P517C/I1050C, D177C/N820C, and L175C/N820C showed high levels of ATPase activity indicates that the protein does not have to adopt an inward-facing conformation with separation of the NBDs for ATP hydrolysis to continue after the first two hydrolysis steps. Login to comment
257 We predict that covalent attachment of thiol-reactive drug substrates to cysteines in the TMDs (or M4M cross-linking of mutants P517C/I1050C, D177C/N820C, or L175C/N820C) traps P-gp in states IV-VI (Fig. 8) that show a high rate of ATP hydrolysis. Login to comment

[hide] Cysteines introduced into extracellular loops 1 an... J Biol Chem. 2014 Sep 5;289(36):24749-58. doi: 10.1074/jbc.M114.583021. Epub 2014 Jul 22. Loo TW, Clarke DM
Cysteines introduced into extracellular loops 1 and 4 of human P-glycoprotein that are close only in the open conformation spontaneously form a disulfide bond that inhibits drug efflux and ATPase activity.
J Biol Chem. 2014 Sep 5;289(36):24749-58. doi: 10.1074/jbc.M114.583021. Epub 2014 Jul 22., [PMID:25053414]

Abstract [show]
P-glycoprotein (P-gp) is an ATP-binding cassette drug pump that protects us from toxic compounds and confers multidrug resistance. The protein is organized into two halves. The halves contain a transmembrane domain (TMD) with six transmembrane segments and a nucleotide-binding domain (NBD). The drug- and ATP-binding sites reside at the TMD1/TMD2 and NBD1/NBD2 interfaces, respectively. ATP-dependent drug efflux involves changes between the open inward-facing (NBDs apart, extracellular loops (ECLs) close together) and the closed outward-facing (NBDs close together, ECLs apart) conformations. It is controversial, however, whether the open conformation only exists transiently in intact cells because of the presence of high levels of ATP. To test for the presence of an open conformation in intact cells, reporter cysteines were placed in extracellular loops 1 (A80C, N half) and 4 (R741C, C half). The rationale was that cysteines A80C/R741C would only come close enough to form a disulfide bond in an open conformation (6.9 A apart) because they are separated widely (30.4 A apart) in the closed conformation. It was observed that the mutant A80C/R741C cross-linked spontaneously (>90%) when expressed in cells. In contrast to previous reports showing that trapping P-gp in a closed conformation highly activated ATPase activity, here we show that A80C/R741C cross-linking inhibited ATPase activity and drug efflux. Both activities were restored when the cross-linked mutant was treated with a thiol-reducing agent. The results show that an open conformation can be readily detected in cells and that cross-linking of cysteines placed in ECLs 1 and 4 inhibits activity.

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Sentences [show]
No. Sentence Comment
257 Direct cross-linking of the cysteines L175C and N820C (23) or cross-linking of mutant P571C/I1050C with the short 1,4-butanediyl bismethanethiosulfonate cross-linker (7.8 &#c5;) (24) highly activated P-gp ATPase activity over 10-fold in the absence of drug substrates. Login to comment
258 Cysteines L175C/N820C are located in the intracellular loops (Fig. 1, C and D), whereas cysteines P517C/I1050C are located in the NBDs (Fig. 1, C and D). Login to comment
259 An explanation for the difference is that linkage of the homologous halves at the L175C/N820C or P517C/I1050C sites would tend to favor the closed conformation (Fig. 1C) to FIGURE 9. Login to comment

[hide] Equilibrated atomic models of outward-facing P-gly... Sci Rep. 2015 Jan 20;5:7880. doi: 10.1038/srep07880. Pan L, Aller SG
Equilibrated atomic models of outward-facing P-glycoprotein and effect of ATP binding on structural dynamics.
Sci Rep. 2015 Jan 20;5:7880. doi: 10.1038/srep07880., [PMID:25600711]

Abstract [show]
P-glycoprotein (Pgp) is an ATP-binding cassette (ABC) transporter that alternates between inward- and outward-facing conformations to capture and force substrates out of cells like a peristaltic pump. The high degree of similarity in outward-facing structures across evolution of ABC transporters allowed construction of a high-confidence outward-facing Pgp atomic model based on crystal structures of outward-facing Sav1866 and inward-facing Pgp. The model adhered to previous experimentally determined secondary- and tertiary- configurations during all-atom molecular dynamics simulations in the presence or absence of MgATP. Three long lasting (>100 ns) meta-stable states were apparent in the presence of MgATP revealing new insights into alternating access. The two ATP-binding pockets are highly asymmetric resulting in differential control of overall structural dynamics and allosteric regulation of the drug-binding pocket. Equilibrated Pgp has a considerably different electrostatic profile compared to Sav1866 that implicates significant kinetic and thermodynamic differences in transport mechanisms.

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Sentences [show]
No. Sentence Comment
203 We did not simulate cross-linking per se, but our structure showed direct side-chain contact between the crosslinked pair LSGGQ (P517C) and Walker A (I1050C) (mouse P513-I1046) showing agreement between our homology model and the biochemical data. Login to comment

[hide] Mapping the Binding Site of the Inhibitor Tariquid... J Biol Chem. 2015 Dec 4;290(49):29389-401. doi: 10.1074/jbc.M115.695171. Epub 2015 Oct 26. Loo TW, Clarke DM
Mapping the Binding Site of the Inhibitor Tariquidar That Stabilizes the First Transmembrane Domain of P-glycoprotein.
J Biol Chem. 2015 Dec 4;290(49):29389-401. doi: 10.1074/jbc.M115.695171. Epub 2015 Oct 26., [PMID:26507655]

Abstract [show]
ABC (ATP-binding cassette) transporters are clinically important because drug pumps like P-glycoprotein (P-gp, ABCB1) confer multidrug resistance and mutant ABC proteins are responsible for many protein-folding diseases such as cystic fibrosis. Identification of the tariquidar-binding site has been the subject of intensive molecular modeling studies because it is the most potent inhibitor and corrector of P-gp. Tariquidar is a unique P-gp inhibitor because it locks the pump in a conformation that blocks drug efflux but activates ATPase activity. In silico docking studies have identified several potential tariquidar-binding sites. Here, we show through cross-linking studies that tariquidar most likely binds to sites within the transmembrane (TM) segments located in one wing or at the interface between the two wings (12 TM segments form 2 divergent wings). We then introduced arginine residues at all positions in the 12 TM segments (223 mutants) of P-gp. The rationale was that a charged residue in the drug-binding pocket would disrupt hydrophobic interaction with tariquidar and inhibit its ability to rescue processing mutants or stimulate ATPase activity. Arginines introduced at 30 positions significantly inhibited tariquidar rescue of a processing mutant and activation of ATPase activity. The results suggest that tariquidar binds to a site within the drug-binding pocket at the interface between the TM segments of both structural wings. Tariquidar differed from other drug substrates, however, as it stabilized the first TM domain. Stabilization of the first TM domain appears to be a key mechanism for high efficiency rescue of ABC processing mutants that cause disease.

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No. Sentence Comment
67 Mutant P517C/I1050C was cross-linked in membranes at 0 &#b0;C with 50 òe;M 1,4-butanediyl bismethanethiosulfonate (BMTS) in the absence or presence of 1 òe;M tariquidar (30). Login to comment
118 The conditions for cross-linking mutants T333C/L975C and P517C/I1050C, however, were different. Login to comment
120 Cross-linking of mutant P517C/I1050C was performed on membranes using BMTS cross-linker (30). Login to comment