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J. Biol. Chem., Vol. 283, Issue 36, 24860-24870, September 5, 2008

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Arginines in the First Transmembrane Segment Promote Maturation of a P-glycoprotein Processing Mutant by Hydrogen Bond Interactions with Tyrosines in Transmembrane Segment 11^*

From the Departments of Medicine and Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada

A key goal is to correct defective folding of mutant ATP binding cassette (ABC) transporters, as they cause diseases such as cystic fibrosis. P-glycoprotein (ABCB1) is a useful model system because introduction of an arginine at position 65 of the first transmembrane (TM) segment could repair folding defects. To determine the mechanism of arginine rescue, we first tested the effects of introducing arginines at other positions in TM1 (residues 52-72) of a P-glycoprotein processing mutant (G251V) that is defective in folding and trafficking to the cell surface (20% maturation efficiency). We found that arginines introduced into one face of the TM1 helix (positions 52, 55, 56, 59, 60, 62, 63, 66, and 67) inhibited maturation, whereas arginines on the opposite face of the helix promoted (positions 64, 65, 68, and 71) or had little effect (positions 61, and 69) on maturation. Arginines at positions 61, 64, 65, and 68 appeared to lie close to the drug binding sites as they reduced the apparent affinity for drug substrates such as vinblastine and verapamil. Therefore, arginines that promoted maturation may face an aqueous drug translocation pathway, whereas those that inhibited maturation may face the lipid bilayer. The highest maturation efficiencies (60-85%) were observed with the Arg-65 and Arg-68 mutants. Mutations that removed hydrogen bond acceptors (Y950F/Y950A or Y953F/Y953A) in TM11 predicted to lie close to Arg-65 or Arg-68 inhibited maturation but did not affect maturation of the G251V parent. Therefore, arginine may rescue defective folding by promoting packing of the TM segments through hydrogen bond interactions.

Received for publication, May 1, 2008 , and in revised form, July 1, 2008.

^* This work was supported by grants from the National Cancer Institute of Canada through the Canadian Cancer Society, Canadian Institutes of Health Research Grants 62832 and 25043, and Cystic Fibrosis Foundation Grant CLARKE-08GO. 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.

¹ Recipient of the Canada Research Chair in Membrane Biology. To whom correspondence should be addressed: Dept. of Medicine, University of Toronto, 1 King's College Circle, Rm. 7342, Medical Sciences Bldg., Toronto, Ontario M5S 1A8, Canada. Tel. or Fax: 416-978-1105; E-mail: david.clarke{at}utoronto.ca.

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