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Head: Jörg H. Kleinschmidt
Biomembranes separate the functional units of living cells. The reserach of this group is focussed on the assembly of biomembranes in general and on the insertion and folding of transmembrane proteins into membranes in particular. These processes are studied using an array of biophysical techniques, such as fluorescence spectroscopy, circular dichroism spectroscopy, electron spin resonance spectroscopy and electrophoresis. We use well defined model systems to investigate membrane assembly and protein insertion and folding in vitro.
Integral membrane proteins are usually very hydrophobic and insoluble in water. It is therefore not trivial to establish a working model system for the study of membrane protein insertion and folding. Whether it is possible at all, depends largely on the properties of the membrane protein. In comparison to the a-helical bundle proteins, the outer membrane proteins that form transmembrane b-barrels have a low average hydrophobicity. Some of these proteins can be denatured completely in a solution of 8 M urea. Hence, they are promising candidates to explore the principles of membrane protein insertion and folding. Insertion and folding often can be accomplished by a strong dilution of the denaturant in the presence of preformed lipid bilayers.
In the past, the research on the mechanism of insertion and folding of b-barrel membrane proteins was mainly focussed on outer membrane protein A of E.coli. This work was performed at the University of Virginia, USA, and some of the results of this research form the basis of many current studies on membrane protein insertion and folding. These www-pages summarize some of the knowledge that we gained on the mechanism of insertion and folding of OmpA.
At present, we are investigating the folding and insertion of the ferric hydroxamat uptake protein component A (FhuA) of E. coli into model membranes. While OmpA forms an 8-stranded b-barrel domain in lipid-bilayers, the structure of FhuA is more complex. The protein consists of a 22-stranded b-barrel domain (554 residues) and of a cork domain (160 residues) that fills out a large volume inside the barrel. We are currently exploring the effect of the cork domain on the insertion and folding of FhuA. Folding studies are performed with wild-type FhuA and with a deletion mutant that does not contain the residues 5 to 160, which form the cork domain in the wild-type protein.
Keywords that characterize the topics and methods in this laboratory: Biomembranes, Membrane Protein Folding and Insertion (Structural changes, Thermodynamics and Kinetics), Membrane Structure, Lipid-Protein Interactions, Protein-Detergent Interactions, Lipid Bilayers, Detergent Micelles, Fluorescence Spectroscopy, Fluorescence Quenching, Electron Spin Resonance Spectroscopy, Site Directed Labelling.
Publications Membrane Protein Folding: Research on the Folding and Insertion of a b-Barrel Membrane Protein (OmpA)
TDFQ (Time Resolved Distance Determination by Fluorescence Quenching) and its Application in Membrane Protein Folding
Structural Motifs of Transmembrane Protein Domains
Small Gallery of b-barrel Membrane Proteins
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