Nano-scale analysis of the drug transport mechanism of MRP1

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Trypsin digests a cytoplasmic loop between the 17th membrane spanning domain and the C-terminal NBD of MRP1. We found that the limited digestion was inhibited in the presence of glutathione (GSH). The inhibitory effect of GSH enhanced by adding of AG-A or Vincristine. The L_0/ICL3 domain was indispensable for the inhibitory effect of GSH. These data suggested GHS interact with the L_0/ICL3 domain and induce a structural change of the C-terminal part of MRP1.We found conserved pairs of Glutamine (507th and 1157th AA(amino acid)) and Glycine (511th and 1161st AA) in the ICL5 (intracellular loop) and the ICL7. These mutant proteins of MRP1 did not have significant structural changes, however lost the transport activity of LTC_4 and could not be photoaffinity labeled with azidoAG-A. The ICL5 mutant MRP1 protein had ATP binding activity of NBD1 but did not that of NBD2. The ICL7 mutant MRP1 protein had lost ATP binding activity in both NBDs. These data suggested that these conserved AAs have important roles in recognition of GSH, binding of ATP and ATPase activity.Some substrates which can be transported with MRP1 without GSH had been reported. However the difference between GSH dependent and independent transport with MRP1 was not clear. SN-38 can be transported with MRP1 in the absence of GSH. We showed one L_0/ICL3 mutant MRP1 which could not transport LTC_4, could transport SN-38. This data suggested the substrates recognition sites of MRP1 may be different between GSH dependent and independent transport at least in part. We also demonstrated that it might be possible to distinguish between GHS dependent or independent substrate on the base of chemical structures.