ABCMdb

ABCB1 p.Phe770Cys

Predicted by SNAP2:	A: N (66%), C: N (82%), D: D (66%), E: D (59%), G: N (57%), H: N (82%), I: N (72%), K: D (59%), L: N (72%), M: N (87%), N: N (66%), P: D (63%), Q: N (72%), R: N (53%), S: N (66%), T: N (66%), V: N (72%), W: D (53%), Y: N (93%),
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: N, Y: N,

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Publications
[hide] The packing of the transmembrane segments of human... J Biol Chem. 2000 Feb 25;275(8):5253-6. Loo TW, Clarke DM
The packing of the transmembrane segments of human multidrug resistance P-glycoprotein is revealed by disulfide cross-linking analysis.
J Biol Chem. 2000 Feb 25;275(8):5253-6., 2000-02-25 [PMID:10681495]

Abstract [show]
Residues from several transmembrane (TM) segments of P-glycoprotein (P-gp) likely form the drug-binding site(s). To determine the organization of the TM segments, pairs of cysteine residues were introduced into the predicted TM segments of a Cys-less P-gp, and the mutant protein was subjected to oxidative cross-linking. In SDS gels, the cross-linked product migrated with a slower mobility than the native protein. The cross-linked products were not detected in the presence of dithiothreitol. Cross-linking was observed in 12 of 125 mutants. The pattern of cross-linking suggested that TM6 is close to TMs 10, 11, and 12, while TM12 is close to TMs 4, 5, and 6. In some mutants the presence of drug substrate colchicine, verapamil, cyclosporin A, or vinblastine either enhanced or inhibited cross-linking. Cross-linking was inhibited in the presence of ATP plus vanadate. These results suggest that the TM segments critical for drug binding must be close to each other and exhibit different conformational changes in response to binding of drug substrate or vanadate trapping of nucleotide. Based on these results, we propose a model for the arrangement of the TM segments.

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No. Sentence Comment
77 In these cross-linking experiments, the amount of oxidant was lowered by 10-fold (0.2 mM), and the minimum temperature required to induce cross-TABLE I Cross-linking analysis of P-gp Cross-linking of S993C (TM12) with residues in the following TM: TM1 TM2 TM3 TM4 TM5 M51C -a Y130C - G185C - G226C - I293C - V52C - I131C - I186C - L227C ϩb T294C - V53C - Q132C - G187C - S228C - A295C ϩ G54C - V133C - D188C - A229C - N296C - T55C - S134C - K189C - A230C - I297C - L56C - F135C - I190C - V231C ϩ S298C - A57C - W136C - G191C - W232C ϩ I299C ϩ A58C - C137C - M192C - A233C ϩ G300C - I59C - L138C - F193C - K234C - A301C - I60C - A139C - F194C - I235C ϩ A302C - H61C - A140C - Q195C - L236C ϩ F303C - G141C - S196C - S237C - L304C - Cross-linking of P350C (TM6) with residues in the following TM: TM7 TM8 TM9 TM10 TM11 F711C - F770C - A828C - I867C - A935C - V712C - F771C - I829C - I868C - H936C - V713C - L772C - G830C - A869C - I937C - G714C - Q773C - S831C - I870C - F938C - V715C - G774C - R832C - A871C - G939C ϩ F716C - F775C - L833C - G872C - I940C - C717C - T776C - A834C - V873C - T941C - A718C - F777C - V835C - V874C ϩ F942C - I719C - G778C - I836C - E875C ϩ S943C - I720C - K779C - T837C - M876C ϩ F944C - N721C - A780C - Q838C - K877C - T945C - G722C - G781C - N839C - M878C - Q946C - G723C - E782C - I840C - L879C - A947C - I783C - a -, no cross-linked product detected in SDS-PAGE. b ϩ, cross-linked product detected in SDS-PAGE. Login to comment

[hide] Disulfide cross-linking analysis shows that transm... J Biol Chem. 2004 Feb 27;279(9):7692-7. Epub 2003 Dec 10. Loo TW, Bartlett MC, Clarke DM
Disulfide cross-linking analysis shows that transmembrane segments 5 and 8 of human P-glycoprotein are close together on the cytoplasmic side of the membrane.
J Biol Chem. 2004 Feb 27;279(9):7692-7. Epub 2003 Dec 10., 2004-02-27 [PMID:14670948]

Abstract [show]
Human P-glycoprotein (P-gp) transports a wide variety of structurally diverse compounds out of the cell. Knowledge about the packing of the transmembrane (TM) segments is essential for understanding the mechanism of drug recognition and transport. We used cysteine-scanning mutagenesis and disulfide cross-linking analysis to determine which TM segment in the COOH half of P-gp was close to TMs 5 and 6 since these segments in the NH(2) half are important for drug binding. An active Cys-less P-gp mutant cDNA was used to generate 240 double cysteine mutants that contained 1 cysteine in TMs 5 or 6 and another in TMs 7 or 8. The mutants were subjected to oxidative cross-linking analysis. No disulfide cross-linking was observed in the 140 TM6/TM7 or TM6/TM8 mutants. By contrast, cross-linking was detected in several P-gp TM5/TM8 mutants. At 4 degrees C, when thermal motion is low, P-gp mutants N296C(TM5)/G774C(TM8), I299C(TM5)/F770C(TM8), I299C(TM5)/G774C(TM8), and G300C(TM5)/F770C(TM8) showed extensive cross-linking with oxidant. These mutants retained drug-stimulated ATPase activity, but their activities were inhibited after treatment with oxidant. Similarly, disulfide cross-linking was inhibited by vanadate trapping of nucleotide. These results indicate that significant conformational changes must occur between TMs 5 and 8 during ATP hydrolysis. We revised the rotational symmetry model for TM packing based on our results and by comparison to the crystal structure of MsbA (Chang, G. (2003) J. Mol. Biol. 330, 419-430) such that TM5 is adjacent to TM8, TM2 is adjacent to TM11, and TMs 1 and 7 are next to TMs 6 and 12, respectively.

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Sentences [show]
No. Sentence Comment
101 Eleven mutants (I293C/F775C, N296C/F770C, N296C/G774C, I297C/F771C, I297C/G774C, I299C/F770C, I299C/G774C, G300C/F767C, G300C/F770C, G300C/F771C, and G300C/G774C) showed relatively strong (Ͼ50%) cross-linking (Table I). Login to comment
105 Six mutants (A295C/ G774C, N296C/F771C, N296C/Q773C, N296C/F775C, I297C/ F770C, and G300C/F775C) showed relatively weak (Ͻ50%) cross-linking (Table I). Login to comment
110 The eleven mutants (I293C/F775C, N296C/F770C, N296C/G774C, I297C/F771C, I297C/G774C, I299C/F770C, I299C/G774C, G300C/F767C, G300C/F770C, G300C/F771C, and G300C/G774C) that showed relatively strong cross-linking at 37 °C were subjected to cross-linking at 22 and 4 °C. Login to comment
111 Only four mutants (N296C/G774C, I299C/F770C, I299C/G774C, and G300C/F770C) still showed cross-linking at 22 and 4 °C. Login to comment
112 Mutants I293C/F775C, N296C/ F770C, I297C/G774C, G300C/F771C, and G300C/G774C were cross-linked only at 22 °C, whereas mutants I297C/F771C and G300C/F767C showed no cross-linking at either 22 or 4 °C. Fig. 3 shows the temperature-dependent cross-linking of mutants N296C/G774C, I299C/F770C, I299C/G774C, and G300C/ F770C. Login to comment
114 All four mutants were cross-linked at a slower rate at 4 °C, with most of the cross-linked product detected by 8 min. Fig. 3 also shows that in mutant N296C/ F770C about 50% of the cross-linked product was detected by 8 min at 22 °C, and cross-linked product was barely detectable after 32 min at 4 °C. Login to comment
115 Mutants N296C/G774C, I299C/F770C, I299C/G774C, and G300C/F770C were selected for further analysis because they were cross-linked at 37, 22, and 4 °C. Login to comment
117 By contrast, no cross-linked product was detected in the single cysteine mutants, N296C, I299C, G300C, F770C, and G774C, when oxidant was added at these temperatures (data not shown). Login to comment
118 To test if the mutants N296C/G774C, I299C/F770C, I299C/ G774C, and G300C/F770C retained the ability to interact with drug substrates, they were expressed in HEK 293 cells, isolated by nickel-chelate chromatography, mixed with lipid, and assayed for drug-stimulated ATPase activity. Login to comment
123 Mutant I299C/F770C had about the same amount of ATPase activity as Cys-less P-gp. Login to comment
124 The verapamiland demecolcine-stimulated ATPase activities rel- TABLE I Cross-linking between residues in TMs 5 and 8 TM5 TM 8 F767C I768C T769C F770C F771C L772C Q773C G774C F775C T776C I293C -a - - - - - - - ϩϩb - T294C - - - - - - - - - - A295C - - - - - - - ϩ - - N296C - - - ϩϩb ϩ - ϩ ϩϩc ϩ - I297C - - - ϩd ϩϩ - - ϩϩb - - S298C - - - - - - - - - - I299C - - - ϩϩc - - - ϩϩc - - G300C ϩϩe - - ϩϩc ϩϩb - - ϩϩb ϩ - A301C - - - - - - - - - - A302C - - - - - - - - - - a No cross-linked product detected in SDS-PAGE gels at 37 °C. b Cross-linked product was also detected at 22 °C. c Cross-linked product was also detected at 22 °C and at 4 °C. d Relatively weak cross-linking (Ͻ50% of P-gp cross-linked) at 37 °C. e Relatively strong cross-linking (Ͼ50% of P-gp cross-linked) at 37 °C. FIG. 2. Login to comment
126 Membranes were prepared from HEK 293 cells expressing P-gp mutants I297C (A), F771C (A), I297C/F771C (A), N296C/F770C (B), or I297C/F770C (B). Login to comment
130 ative to that of Cys-less P-gp were 65 and 62%, 68 and 51%, and 57 and 79% for mutants N296C/G774C, I299C/G774C, and G300C/F770C, respectively. Login to comment
131 We then tested whether cross-linking affected the verapamil-stimulated ATPase activities of mutants N296C/G774C, I299C/ F770C, I299C/G774C, and G300C/F770C. Login to comment
134 By contrast, the verapamil-stimulated ATPase activities of mutants N296C/G774C, I299C/ F770C, I299C/G774C, and G300C/F770C were inhibited by 60-80% after treatment with oxidant. These results suggest that cross-linking inhibits conformational changes in P-gp during ATP hydrolysis (47, 50). Login to comment
135 Because there is evidence that TM5 lines the drug binding pocket of P-gp (44), we tested whether drug substrates that stimulate (demecolcine and verapamil) or inhibit (cyclosporin A) (29) ATPase activity would affect the cross-linking pattern observed in mutants N296C/G774C, I299C/F770C, I299C/ G774C, and G300C/F770C. Login to comment
138 Mutant I299C/F770C showed a small decrease in cross-linking with cyclosporin A and demecolcine, whereas mutant I299C/ G774C was only slightly affected by the drug substrates. Login to comment
139 Mutants G300C/F770C showed the largest decrease in cross-linking with cyclosporin A. Login to comment
147 Accordingly, the effect of vanadate trapping on cross-linking of mutants N296C/G774C, I299C/ F770C, I299C/G774C, and G300C/F770C was examined. Login to comment
151 Effect of temperature on cross-linking. Membranes were prepared from HEK 293 cells expressing P-gp mutants N296C/G774C, I299C/F770C, I299C/G774C, G300C/F770C, or N296C/F770C. Login to comment
157 Histidine-tagged Cys-less (C-less) P-gp and mutants N296C/ G774C, I299C/F770C, I299C/G774C, or G300C/F770C were isolated by nickel-chelate chromatography. Login to comment
162 Effect of drug substrates on cross-linking. Membranes were prepared from HEK 293 cells expressing P-gp mutants N296C/ G774C, I299C/F770C, I299C/G774C, or G300C/F770C. Login to comment
191 The model may explain why the presence of drug substrates had relatively little effect on cross-linking of mutants N296C/ G774C, I299C/F770C, I299C/G774C, and G300C/F770C. Login to comment
197 Membranes from HEK 293 cells expressing P-gp mutants N296C/G774C, I299C/F770C, I299C/G774C, or G300C/F770C were preincubated at 37 °C for 10 min in the presence (ϩ) or absence (-) of ATP and MgCl2 plus sodium vanadate (ATP/VO4). Login to comment
211 For example, vanadate trapping of nucleotide nearly abolished cross-linking in mutants N296C/ G774C, I299C/F770C, I299C/G774C, and G300C/F770C (Fig. 6), although cross-linking inhibited drug-stimulated ATPase activity. Login to comment

[hide] The drug-binding pocket of the human multidrug res... Biochemistry. 2004 Sep 28;43(38):12081-9. Loo TW, Bartlett MC, Clarke DM
The drug-binding pocket of the human multidrug resistance P-glycoprotein is accessible to the aqueous medium.
Biochemistry. 2004 Sep 28;43(38):12081-9., 2004-09-28 [PMID:15379547]

Abstract [show]
P-Glycoprotein (P-gp) is an ATP-dependent drug pump that transports a broad range of compounds out of the cell. Cross-linking studies have shown that the drug-binding pocket is at the interface between the transmembrane (TM) domains and can simultaneously bind two different drug substrates. Here, we determined whether cysteine residues within the drug-binding pocket were accessible to the aqueous medium. Cysteine mutants were tested for their reactivity with the charged thiol-reactive compounds sodium (2-sulfonatoethyl)methanethiosulfonate (MTSES) and [2-(trimethylammonium)ethyl)]methanethiosulfonate (MTSET). Residue Ile-306(TM5) is close to the verapamil-binding site. It was changed to cysteine, reacted with MTSES or MTSET, and assayed for verapamil-stimulated ATPase activity. Reaction of mutant I306C(TM5) with either compound reduced its affinity for verapamil. We confirmed that the reduced affinity for verapamil was indeed due to introduction of a charge at position 306 by demonstrating that similar effects were observed when Ile-306 was replaced with arginine or glutamic acid. Mutant I306R showed a 50-fold reduction in affinity for verapamil and very little change in the affinity for rhodamine B or colchicine. MTSES or MTSET modification also affected the cross-linking pattern between pairs of cysteines in the drug-binding pocket. For example, both MTSES and MTSET inhibited cross-linking between I306C(TM5) and I868C(TM10). Inhibition was enhanced by ATP hydrolysis. By contrast, cross-linking of cysteine residues located outside the drug-binding pocket (such as G300C(TM5)/F770C(TM8)) was not affected by MTSES or MTSET. These results indicate that the drug-binding pocket is accessible to water.

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No. Sentence Comment
231 Not all cysteines in the TM domains were accessible for modification by MTSES or MTSET. Cross-linking of mutants G300C(TM5)/F770C- (TM8) or C137C(TM2)/I935C(TM11), the cysteines of which are located outside the drug-binding pocket, was not affected by MTSES or MTSET. Login to comment