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Journal of Bacteriology, July 2008, p. 4568-4575, Vol. 190, No. 13
0021-9193/08/$08.00+0     doi:10.1128/JB.00369-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Omp85_Tt from Thermus thermophilus HB27: an Ancestral Type of the Omp85 Protein Family

Jutta Nesper,^1* Alexander Brosig,¹ Philippe Ringler,^2, Geetika J. Patel,^1, Shirley A. Müller,² Jörg H. Kleinschmidt,¹ Winfried Boos,¹ Kay Diederichs,¹ and Wolfram Welte¹

Department of Biology, University of Konstanz, 78457 Konstanz, Germany,¹ Maurice E. Müller Institute, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland²

Received 13 March 2008/ Accepted 18 April 2008

Proteins belonging to the Omp85 family are involved in the assembly of β-barrel outer membrane proteins or in the translocation of proteins across the outer membrane in bacteria, mitochondria, and chloroplasts. The cell envelope of the thermophilic bacterium Thermus thermophilus HB27 is multilayered, including an outer membrane that is not well characterized. Neither the precise lipid composition nor much about integral membrane proteins is known. The genome of HB27 encodes one Omp85-like protein, Omp85_Tt, representing an ancestral type of this family. We overexpressed Omp85_Tt in T. thermophilus and purified it from the native outer membranes. In the presence of detergent, purified Omp85_Tt existed mainly as a monomer, composed of two stable protease-resistant modules. Circular dichroism spectroscopy indicated predominantly β-sheet secondary structure. Electron microscopy of negatively stained lipid-embedded Omp85_Tt revealed ring-like structures with a central cavity of 1.5 nm in diameter. Single-channel conductance recordings indicated that Omp85_Tt forms ion channels with two different conducting states, characterized by conductances of 0.4 nS and 0.65 nS, respectively.

Published ahead of print on 2 May 2008.

These authors contributed equally to this work.