NIH Research Festival
P-glycoprotein (P-gp, ABCB1), which is linked to cancer multidrug resistance, transports a variety of amphipathic chemically dissimilar compounds including anticancer drugs out of cells by using the energy from ATP hydrolysis. The mechanism linking ATP hydrolysis to the transport cycle of P-gp still remains unclear. An oxidative crosslinker, copper-1-10-phenenthroline (Cu-phe), was used to elucidate the conformational states of P-gp during its catalytic cycle. Of the seven cysteine residues located at various positions within P-gp, C431 and C1074, located within the Walker A motifs of nucleotide-binding domains (NBDs) could be cross-linked in the presence of Cu-Phe. Therefore, we used these residues as reporter sites to study the conformational changes associated with the catalytic cycle of P-gp. Cu-phe was not able to crosslink wild-type (WT) P-gp in the ADP-vanadate trapped conformation. However, partial crosslinking of an ATP hydrolysis-defective mutant of P-gp (E556Q/E1201Q) was observed. In addition, ADP alone did not inhibit the crosslinking of WT P-gp, while AMP-PNP, ADP-vanadate and AMP-PNP-vanadate were able to inhibit the crosslinking induced by Cu-Phe for WT P-gp. This was in contrast to the E556Q/E1201Q mutant, for which, a partial crosslinking was observed in the presence of all nucleotides, irrespective of the presence or absence of vanadate, suggesting that the conformation of E556Q/E1201Q mutant NBDs might be different compared to WT NBDs. The data in aggregate demonstrate that crosslinking of cysteine residues induced by Cu-phe can be used to probe conformational changes in ATP sites during the ATP hydrolysis cycle of P-gp.
Scientific Focus Area: Molecular Biology and Biochemistry
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