P-glycoprotein function involves conformational transitions detectable by differential immunoreactivity.
The MDR1 P-glycoprotein (Pgp), a member of the ATP-binding cassette family of transporters, is a transmembrane ATPase efflux pump for various lipophilic compounds, including many anti-cancer drugs. mAb UIC2, reactive with the extracellular moiety of Pgp, inhibits Pgp-mediated efflux. UIC2 reactivity with Pgp was increased by the addition of several Pgp-transported compounds or ATP-depleting agents, and by mutational inactivation of both nucleotide-binding domains (NBDs) of Pgp. UIC2 binding to Pgp mutated in both NBDs was unaffected in the presence of Pgp transport substrates or in ATP-depleted cells, whereas the reactivities of the wild-type Pgp and Pgps mutated in a single NBD were increased by these treatments to the level of the double mutant. These results indicate the existence of different Pgp conformations associated with different stages of transport-associated ATP hydrolysis and suggest trapping in a transient conformation as a mechanism for antibody-mediated inhibition of Pgp.
Mechetner
E B
EB
Department of Molecular Genetics, University of Illinois, Chicago 60607-7170, USA.
Schott
B
B
Morse
B S
BS
Stein
W D
WD
Druley
T
T
Davis
K A
KA
Tsuruo
T
T
Roninson
I B
IB
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D001692:Biological Transport; D006801:Humans; D006868:Hydrolysis; D011485:Protein Binding; D011487:Protein Conformation; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D000255:Adenosine Triphosphate