TtOmp85 from Thermus thermophilus HB27: An ancestral type of the Omp85 protein family

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

^* To whom correspondence should be addressed. Email: Jutta.Nesper{at}uni-konstanz.de.

	Abstract

Proteins belonging to the Omp85 family are involved in the assembly of -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, TtOmp85, representing an ancestral type of this family. We overexpressed TtOmp85 in T. thermophilus and purified it from the native outer membranes. In the presence of detergent, purified TtOmp85 existed mainly as a monomer, composed of two stable protease resistant modules. Circular dichroism spectroscopy indicated -sheet secondary structure. Electron microscopy of negatively stained lipid embedded TtOmp85 revealed ring-like structures with a central cavity of 1.5 nm in diameter. Single channel conductance recordings indicated that TtOmp85 forms ion channels with two different conducting states, characterized by conductances of 0.4 nS and 0.65 nS, respectively.