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Antibody C219 Recognizes an α -Helical Epitope on P-Glycoprotein

Jean M. H. Van den Elsen, Douglas A. Kuntz, Flip J. Hoedemaeker and David R. Rose
Proceedings of the National Academy of Sciences of the United States of America
Vol. 96, No. 24 (Nov. 23, 1999), pp. 13679-13684
Stable URL: http://www.jstor.org/stable/121281
Page Count: 6
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Antibody C219 Recognizes an α -Helical Epitope on P-Glycoprotein
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Abstract

The ABC transporter, P-glycoprotein, is an integral membrane protein that mediates the ATP-driven efflux of drugs from multidrug-resistant cancer and HIV-infected cells. Anti-P-glycoprotein antibody C219 binds to both of the ATP-binding regions of P-glycoprotein and has been shown to inhibit its ATPase activity and drug binding capacity. C219 has been widely used in a clinical setting as a tumor marker, but recent observations of cross-reactivity with other proteins, including the c-erbB2 protein in breast cancer cells, impose potential limitations in detecting P-glycoprotein. We have determined the crystal structure at a resolution of 2.4 angstrom of the variable fragment of C219 in complex with an epitope peptide derived from the nucleotide binding domain of P-glycoprotein. The 14-residue peptide adopts an amphipathic α -helical conformation, a secondary structure not previously observed in structures of antibody-peptide complexes. Together with available biochemical data, the crystal structure of the C219-peptide complex indicates the molecular basis of the cross-reactivity of C219 with non-multidrug resistance-associated proteins. Alignment of the C219 epitope with the recent crystal structure of the ATP-binding subunit of histidine permease suggests a structural basis for the inhibition of the ATP and drug binding capacity of P-glycoprotein by C219. The results provide a rationale for the development of C219 mutants with improved specificity and affinity that could be useful in antibody-based P-glycoprotein detection and therapy in multidrug resistant cancers.

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