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Journal of Bacteriology, June 2002, p. 3313-3320, Vol. 184, No. 12
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.12.3313-3320.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Membrane Topology of the Multidrug Transporter MdfA: Complementary Gene Fusion Studies Reveal a Nonessential C-Terminal Domain

Julia Adler and Eitan Bibi*

Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel

Received 22 January 2002/ Accepted 20 March 2002

The hydrophobicity profile and sequence alignment of the Escherichia coli multidrug transporter MdfA indicate that it belongs to the 12-transmembrane-domain family of transporters. According to this prediction, MdfA contains a single membrane-embedded charged residue (Glu26), which was shown to play an important role in substrate recognition. To test the predicted secondary structure of MdfA, we analyzed complementary pairs of hybrids of MdfA-PhoA (alkaline phosphatase, functional in the periplasm) and MdfA-Cat (chloramphenicol acetyltransferase, functional in the cytoplasm), generated in all the putative cytoplasmic and periplasmic loops of MdfA. Our results support the 12-transmembrane topology model and the suggestion that except for Glu26, no other charged residues are present in the membrane domain of MdfA. Surprisingly, by testing the ability of the truncated MdfA-Cat and MdfA-PhoA hybrids to confer multidrug resistance, we demonstrate that the entire C-terminal transmembrane domain and the cytoplasmic C terminus are not essential for MdfA-mediated drug resistance and transport.

* Corresponding author. Mailing address: Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel. Phone and fax: 972-8-9343464. E-mail: bcbibi{at}wicc.weizmann.ac.il.

Journal of Bacteriology, June 2002, p. 3313-3320, Vol. 184, No. 12
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.12.3313-3320.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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