ABCMdb

PMID: 17237262

Sauna ZE, Ambudkar SV
About a switch: how P-glycoprotein (ABCB1) harnesses the energy of ATP binding and hydrolysis to do mechanical work.
Mol Cancer Ther. 2007 Jan;6(1):13-23., [PubMed]

Sentences

No. Mutations Sentence Comment

90 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln In human Pgp, the double-mutant E556Q/E1201Q does not show steady-state hydrolysis but can occlude the nucleoside triphosphate in a reaction intermediate (21, 55). Login to comment 106 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln Figure 1 shows likely transition states during the formation of the occluded conformation, which occurs in mutants of Pgp where both ''catalytic carboxylates`` have been altered (E556Q/E1201Q for human Pgp). Login to comment 112 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln By using the E599Q mutant (equivalent to the human Pgp mutant E556Q/ E1201Q described above) and site-specific labeling with a fluorophore, they were able to monitor the kinetics of the occlusion in real time and obtain initial rates. Login to comment 198 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln However, it is not clear from these data whether the nonhydrolyzable analogues of ATP represent the ''nucleotide bound`` state or the ''occluded nucleotide`` state of Pgp. Recent work from our laboratory (58) suggests that the formation of the ATP-occluded conformation of the mutant human Pgp E556Q/E1201Q is energy dependent with an activation energy of f70 kJ/mol, a value that is comparable with that obtained for ATP-driven dimerization of an equivalent mutant of Mdl1 (50). Login to comment 200 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln We have furthermore shown that occlusion of ATP in the mutant human Pgp E556Q/E1201Q is accompanied by a decreased binding of transport substrate. Login to comment 254 ABCB1 p.Glu1201Gln ABCB1 p.Glu556Gln Conformational changes in the drug-binding sites during the different reaction intermediates of the ATPase reaction mediated by Pgp Reaction intermediate Trapped intermediate Effect on drug-binding site References E + S Pgp + ATP No effect on IAAP binding (34, 70) E.S Pgp (E556Q/E1201Q).ATP Reduced affinity for IAAP (55, 58) Pgp.AMPPNP Reduced affinity for vinblastine (67, 69) Structural changes in transmembrane domains observed by electron microscopy (67, 78) Conformational changes using the antibody UIC2 (67) Pgp.ATP-g-S Reduced affinity for vinblastine (68) and * E.P Pgp.ADP.Vi Reduced affinity for IAAP (34, 35, 37, 55, 70) Reduced affinity for vinblastine (67-69) Structural changes in transmembrane domains observed by electron microscopy (67, 78) Conformational changes using the antibody UIC2 (67, 79, 80) Rotation of helices TM6 and TM12 (76) E + P Pgp + ADP + Vi (Pi) Reduced affinity for IAAP (34, 35) *Sauna and Ambudkar, unpublished data. Login to comment