Localization of the iodomycin binding site in hamster P-glycoprotein.
P-glycoprotein, the overexpression of which is a major cause for the failure of cancer chemotherapy in man, recognizes and transports a broad range of structurally unrelated amphiphilic compounds. This study reports on the localization of the binding site of P-glycoprotein for iodomycin, the Bolton-Hunter derivative of the anthracycline daunomycin. Plasma membrane vesicles isolated from multidrug-resistant Chinese hamster ovary B30 cells were photolabeled with [125I]iodomycin. After chemical cleavage behind the tryptophan residues, 125I-labeled peptides were separated by electrophoresis and high performance liquid chromatography. Edman sequencing revealed that [125I]iodomycin had been predominantly incorporated into the fragment 230-312 of isoform I of hamster P-glycoprotein. According to models based on hydropathy plots, the amino acid sequence 230-312 forms the distal part of transmembrane segment 4, the second cytoplasmic loop, and the proximal part of transmembrane segment 5 in the N-terminal half of P-glycoprotein. The binding site for iodomycin is recognized with high affinity by vinblastine and cyclosporin A.
Demmer
A
A
Klinische Forschergruppe, Zentrum Biochemie and Zentrum Kinderheilkunde, OE 4350, Medizinische Hochschule Hannover, D-30623 Hannover, Germany.
Thole
H
H
Kubesch
P
P
Brandt
T
T
Raida
M
M
Fislage
R
R
Tümmler
B
B
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000345:Affinity Labels; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D003630:Daunorubicin / Q000031:analogs & derivatives* / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D014357:Trypsin / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D010446:Peptide Fragments; C060588:iodomycin; D014357:Trypsin; D003630:Daunorubicin