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Journal of Bacteriology, March 2002, p. 1417-1422, Vol. 184, No. 5
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.5.1417-1422.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Disruption of lolCDE, Encoding an ATP-Binding Cassette Transporter, Is Lethal for Escherichia coli and Prevents Release of Lipoproteins from the Inner Membrane

*** Shin-ichiro Narita,{dagger}, Kimie Tanaka, Shin-ichi Matsuyama, and Hajime Tokuda*

Institute of Molecular and Cellular Biosciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan

Received 16 July 2001/ Accepted 28 November 2001

ATP-binding cassette transporter LolCDE was previously identified, by using reconstituted proteoliposomes, as an apparatus catalyzing the release of outer membrane-specific lipoproteins from the inner membrane of Escherichia coli. Mutations resulting in defective LolD were previously shown to be lethal for E. coli. The amino acid sequences of LolC and LolE are similar to each other, but the necessity of both proteins for lipoprotein release has not been proved. Moreover, previous reconstitution experiments did not clarify whether or not LolCDE is the sole apparatus for lipoprotein release. To address these issues, a chromosomal lolC-lolD-lolE null mutant harboring a helper plasmid that carries the lolCDE genes and a temperature-sensitive replicon was constructed. The mutant failed to grow at a nonpermissive temperature because of the depletion of LolCDE. In addition to functional LolD, both LolC and LolE were required for growth. At a nonpermissive temperature, the outer membrane lipoproteins were mislocalized in the inner membrane since LolCDE depletion inhibited the release of lipoproteins from the inner membrane. Furthermore, both LolC and LolE were essential for the release of lipoproteins. On the other hand, LolCDE depletion did not affect the translocation of a lipoprotein precursor across the inner membrane and subsequent processing to the mature lipoprotein. From these results, we conclude that the LolCDE complex is an essential ABC transporter for E. coli and the sole apparatus mediating the release of outer membrane lipoproteins from the inner membrane.

* Corresponding author. Mailing address: Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. Phone: 81-3-5841-7830. Fax: 81-3-5841-8464. E-mail: htokuda{at}iam.u-tokyo.ac.jp.

{dagger} Present address: Department of Molecular Life Science, Tokai University School of Medicine, Isehara 259-1193, Japan.

Journal of Bacteriology, March 2002, p. 1417-1422, Vol. 184, No. 5
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.5.1417-1422.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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