... helixextending from the TMD, may be involved in signaltransduction between the TMD and NBD, by sens-ing either hydrolysis of the terminal phosphate or the presence of substrate in the drug-binding ... E552 in NBD1 and E1197 in NBD2. Tofurther characterize the role of these residues in catalysis, we created in Abcb1a the single-site mutants E552D, N and A in NBD1, and E1197D,N and A in NBD2, ... trapped in these proteins. To answer thisquestion, we took advantage of the trypsin-sensitiveregion situated in the linker domain of Abcb1a. Fol-lowing trapping in the absence or presence of Vi and mild-trypsin...