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J. Biol. Chem., Vol. 279, Issue 51, 53571-53583, December 17, 2004

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Identification and Characterization of Functionally Important Elements in the Multidrug Resistance Protein 1 COOH-terminal Region^*

Christopher J. Westlake¶, Lea Payen, Mian Gao, Susan P. C. Cole||**, and Roger G. Deeley, The Stauffer Professor of Basic Oncology at Queen's University||

From the Department of Biochemistry, the ^||Department of Pathology and Molecular Medicine, and the Cancer Research Institute, Queen's University, Kingston, Ontario K7L 3N6, Canada

The ATP binding cassette (ABC) transporter, multidrug resistance protein 1 (MRP1/ABCC1), transports a broad spectrum of conjugated and unconjugated compounds, including natural product chemotherapeutic agents. In this study, we have investigated the importance of the COOH-terminal region of MRP1 for transport activity and basolateral plasma membrane trafficking. The COOH-terminal regions of some ABCC proteins have been implicated in protein trafficking, but the function of this region of MRP1 has not been defined. In contrast to results obtained with other ABCC proteins, we found that the COOH-proximal 30 amino acids of MRP1 can be removed without affecting trafficking to basolateral membranes. However, the truncated protein is inactive. Furthermore, removal of as few as 4 COOH-terminal amino acids profoundly decreases transport activity. Although amino acid sequence conservation of the COOH-terminal regions of ABC proteins is low, secondary structure predictions indicate that they consist of a broadly conserved helix-sheet-sheet-helix-helix structure. Consistent with a conservation of secondary and tertiary structure, MRP1 hybrids containing the COOH-terminal regions of either the homologous MRP2 or the distantly related P-glycoprotein were fully active and trafficked normally. Using mutated proteins, we have identified structural elements containing five conserved hydrophobic amino acids that are required for activity. We show that these are important for binding and hydrolysis of ATP by nucleotide binding domain 2. Based on crystal structures of several ABC proteins, we suggest that the conserved amino acids may stabilize a helical bundle formed by the COOH-terminal three helices and may contribute to interactions between the COOH-terminal region and the protein's two nucleotide binding domains.

Received for publication, March 5, 2004 , and in revised form, August 31, 2004.

^* This work was supported by a grant from the National Cancer Institute of Canada with funds from the Terry Fox Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ Recipient of an Ontario Graduate Scholarship.

^** The Canada Research Chair in Cancer Biology.

To whom correspondence should be addressed: Cancer Research Institute, Botterell Hall, Queen's University, Kingston, Ontario K7L 3N6, Canada. Tel.: 613-533-2979; Fax: 613-533-6830; E-mail: deeleyr{at}post.queensu.ca.

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