ABCMdb

ABCC1 p.Ile441Leu

Predicted by SNAP2:	A: D (63%), C: N (57%), D: D (91%), E: D (85%), F: N (66%), G: D (80%), H: D (85%), K: D (91%), L: N (87%), M: D (53%), N: D (85%), P: D (91%), Q: D (75%), R: D (91%), S: D (59%), T: D (75%), V: N (53%), W: D (75%), Y: D (80%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: N, 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] Structural determinants of substrate specificity d... Drug Metab Dispos. 2008 Dec;36(12):2571-81. Epub 2008 Sep 5. Grant CE, Gao M, DeGorter MK, Cole SP, Deeley RG
Structural determinants of substrate specificity differences between human multidrug resistance protein (MRP) 1 (ABCC1) and MRP3 (ABCC3).
Drug Metab Dispos. 2008 Dec;36(12):2571-81. Epub 2008 Sep 5., [PMID:18775981]

Abstract [show]
Multidrug resistance proteins (MRPs) are members of the "C" branch of the ATP-binding cassette transporter superfamily. Human MRP1 transports a wide range of natural product drugs and structurally diverse conjugated and unconjugated organic anions. Its closest relative is MRP3. Despite their structural similarity, the homologs differ substantially in their substrate specificity. It is noteworthy that MRP1 transports glutathione (GSH) and GSH conjugates and displays GSH-stimulated transport of a number of unconjugated and conjugated compounds. In contrast, MRP3 does not transport GSH and is a poor transporter of GSH conjugates. However, both proteins transport glucuronide conjugates, such as 17beta-estradiol 17-(beta-D-glucuronide). We have constructed a series of MRP1/MRP3 hybrids and used them to identify a region of MRP1 that is critical for binding and transport of GSH conjugates such as leukotriene C(4) (LTC(4)). Substitution of this region encompassing transmembrane helices 8 and 9 and portions of cytoplasmic loops 4 and 5 of MRP1 with the equivalent region of MRP3 eliminated LTC(4) transport. Transport of other substrates was either unaffected or enhanced. We identified three residues in this region: Tyr(440), Ile(441), and Met(443), mutation of which differentially affected transport. It is noteworthy that substitution of Tyr(440) with Phe, as found in MRP3, reduced LTC(4) and GSH-stimulated estrone-3-sulfate transport without affecting transport of other substrates tested. The mutation increased the K(m) for LTC(4) 5-fold and substantially reduced photolabeling of MRP1 by both [3H]LTC(4) and the GSH derivative, azidophenacyl-[35S]GSH. These results suggest that Tyr(440) makes a major contribution to recognition of GSH and the GSH moiety of conjugates such as LTC(4).

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No. Sentence Comment
138 The most dramatic reduction in transport was found for one double mutation located in the G1 region, Y440F/I441L, which reduced LTC4 transport to less than 20% of wild-type levels (Fig. 3B). Login to comment
142 With the exception of one triple mutation, in which substitution of M443 with L was introduced into the LTC4 transport-deficient Y440F/I441L double mutant, no combination of mutations tested reduced LTC4 transport by more than 60 to 70% (data not shown). Login to comment
143 The Y440F/I441L/M443L virtually eliminated LTC4 transport (Fig. 3B) but also reduced E217betaG transport by approximately 80% (Fig. 3C). Login to comment
144 Transport of LTC4, E217betaG, E13SO4, and MTX by Y440F, I441L, and M443L MRP1 Mutant Proteins. Login to comment
156 The Y440F and M443L mutations each independently decreased initial rates of LTC4 transport by approximately 60 and 50%, respectively, whereas the I441L mutation had little or no effect (Fig. 3B). Login to comment
157 In contrast, E217betaG transport was decreased approximately 50% by both the I441L and M443L mutations but only 20% by the Y440F mutation (Fig. 3C). Login to comment
158 All three mutations significantly decreased E13SO4 transport in the presence of 2 mM S-methyl GSH, with the Y440F, I441L, and M443L mutations reducing transport at 1 min by approximately 65, 50, and 90%, respectively (Fig. 3D). Login to comment
175 Kinetic Parameters of [3 H]LTC4 Transport by Y440F and I441L Single and Double Mutants. Login to comment
176 We also determined the effects of the Y440F and I441L single and double mutations on the Km and Vmax for LTC4 transport. Login to comment
179 Although LTC4 transport by the I441L mutant was only marginally decreased at a fixed concentration of substrate, linear regression analysis indicated that the Km for LTC4 was increased approximately 2-fold (149 nM for the I441L mutant protein versus 72 nM for wild-type MRP1), again with no significant change in Vmax (normalized Vmax for the I441L mutation 42 versus 37 pmol/mg/min for the wild-type protein) (Fig. 4, A and B). Login to comment
200 Photolabeling of both fragments of the I441L mutant protein, which displayed only a 2-fold increase in Km, was essentially indistinguishable from that obtained with the wild-type MRP1 protein. Login to comment
201 However, photolabeling of the NH2-terminal fragments of both the Y440F and double Y440F/I441L mutant proteins was similarly, substantially reduced compared with both the wild-type and the I441L mutant. Login to comment
203 Furthermore, photolabeling of the COOH-terminal fragment of the Y440F and Y440F/I441L mutant proteins was also reduced when compared with wild-type MRP1 or the I441L mutant, despite the fact that this region is identical in all four proteins. Login to comment
222 Shown are wild-type MRP1 (f), Y440F (Œ), I441L (), and Y440F/I441L (ࡗ). Login to comment
226 [3 H]LTC4 photolabeling of membrane vesicle isolated from Sf21 cells expressing wild-type and mutant MRP1 proteins. A, immunoblot showing the relative amounts of MRP1 protein in each sample after adjustment for relative MRP1 protein expression; wild-type MRP1 (35 ␮g) and mutants Y440F (75 ␮g), I441L (22 ␮g), and Y440F/I441L (20 ␮g). Login to comment
238 In contrast, the I441L mutant protein, which decreased S-methyl GSH-stimulated transport of E13SO4 by 55% compared with wild-type MRP1 (Fig. 3D), bound approximately equivalent levels of azidophenacyl-[35 S]GSH (Fig. 7C), suggesting that, as was determined for LTC4, the affinity for azidophenacyl-GSH is relatively unaffected by the I441L mutation. Login to comment
242 Effect of the Y440F, I441L, M443L, and Y440F/I441L Mutations on Resistance to Vincristine, Doxorubicin, and VP-16. Login to comment
243 Lastly, the drug-resistance profiles of Y440F, I441L, M443L, and Y440F/I441L mutant proteins were examined because unlike MRP1, the profile of resistance to natural product drugs conferred by MRP3 is restricted primarily to epipodophyllotoxins (Deeley et al., 2006). Login to comment
295 In contrast to the Y440F mutation, the conservatively substituted I441L mutation had no effect on LTC4 or MTX transport but decreased transport of both E217betaG and E13SO4, whereas the M443L mutation decreased transport of all three conjugated substrates but not TABLE 2 Relative Drug Resistance of HEK293 Cells Transfected with Wild-Type and Mutant MRP1 Transfectant Drug (Relative Resistance Factora ) Vincristine VP-16 Doxorubicin HEKMRP1 15.6 Ϯ 2.5 16.2 Ϯ 4.9 4.5 Ϯ 0.3 HEKMRP1-Y440F 2.4 Ϯ 0.5 (5.1) 2.7 Ϯ 0.8 (6.0) 1.3 Ϯ 0.2 (1.9) HEKMRP1-1441L 8.9 Ϯ 2.5 (9.7) 4.1 Ϯ 1.2 (4.4) 3.7 Ϯ 1.4 (4.1) HEKMRP1-M443L 6.5 Ϯ 1.2 (6.0) 5.8 Ϯ 0.5 (5.4) 3.8 Ϯ 0.7 (3.6) HEKMRP1-Y440F/1441L 3.9 Ϯ 1.0 (7.5) 1.3 Ϯ 0.3 (1.7) 1.2 Ϯ 0.2 (1.5) HEKMRP3 1.1 Ϯ 0.1 6.4 Ϯ 1.9 0.87 Ϯ 0.2 a The relative resistance factor was obtained by dividing the IC50 values for the wild-type or mutant MRP1-transfected cells by the IC50 value for cells transfected with the expression vector alone. Login to comment

[hide] Structural and functional properties of human mult... Curr Med Chem. 2011;18(3):439-81. He SM, Li R, Kanwar JR, Zhou SF
Structural and functional properties of human multidrug resistance protein 1 (MRP1/ABCC1).
Curr Med Chem. 2011;18(3):439-81., [PMID:21143116]

Abstract [show]
Multidrug ABC transporters such as P-glycoprotein (P-gp/MDR1/ABCB1) and multidrug resistance protein 1 (MRP1/ABCC1) play an important role in the extrusion of drugs from the cell and their overexpression can be a cause of failure of anticancer and antimicrobial chemotherapy. Recently, the mouse P-gp/Abcb1a structure has been determined and this has significantly enhanced our understanding of the structure-activity relationship (SAR) of mammalian ABC transporters. This paper highlights our current knowledge on the structural and functional properties and the SAR of human MRP1/ABCC1. Although the crystal structure of MRP1/ABCC1 has yet to be resolved, the current topological model of MRP1/ABCC1 contains two transmembrane domains (TMD1 and TMD2) each followed by a nucleotide binding domain (NBD) plus a third NH2-terminal TMD0. MRP1/ABCC1 is expressed in the liver, kidney, intestine, brain and other tissues. MRP1/ABCC1 transports a structurally diverse array of important endogenous substances (e.g. leukotrienes and estrogen conjugates) and xenobiotics and their metabolites, including various conjugates, anticancer drugs, heavy metals, organic anions and lipids. Cells that highly express MRP1/ABCC1 confer resistance to a variety of natural product anticancer drugs such as vinca alkaloids (e.g. vincristine), anthracyclines (e.g. etoposide) and epipodophyllotoxins (e.g. doxorubicin and mitoxantrone). MRP1/ABCC1 is associated with tumor resistance which is often caused by an increased efflux and decreased intracellular accumulation of natural product anticancer drugs and other anticancer agents. However, most compounds that efficiently reverse P-gp/ABCB1-mediated multidrug resistance have only low affinity for MRP1/ABCC1 and there are only a few effective and relatively specific MRP1/ABCC1 inhibitors available. A number of site-directed mutagenesis studies, biophysical and photolabeling studies, SAR and QSAR, molecular docking and homology modeling studies have documented the role of multiple residues in determining the substrate specificity and inhibitor selectivity of MRP1/ABCC1. Most of these residues are located in the TMs of TMD1 and TMD2, in particular TMs 4, 6, 7, 8, 10, 11, 14, 16, and 17, or in close proximity to the membrane/cytosol interface of MRP1/ABCC1. The exact transporting mechanism of MRP1/ABCC1 is unclear. MRP1/ABCC1 and other multidrug transporters are front-line mediators of drug resistance in cancers and represent important therapeutic targets in future chemotherapy. The crystal structure of human MRP1/ABCC1 is expected to be resolved in the near future and this will provide an insight into the SAR of MRP1/ABCC1 and allow for rational design of anticancer drugs and potent and selective MRP1/ABCC1 inhibitors.

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No. Sentence Comment
794 In addition, the Tyr440Phe, Ile441Leu, Met443Leu mutations decreased resistance to vincristine and etoposide 2-to 3-fold, whereas only the Tyr440Phe mutant displayed a major decrease in resistance to doxorubicin [374]. Login to comment