Current Research

The labs interest focuses on 1) the structure and function of proton pumping ATPases and 2) on the design and redesign of proteins with novel functions and architectures. In both research areas we employ a multidisciplinary strategy including X-ray crystallography to characterize the molecules.

1) The vacuolar ATPase of Saccharomyces Cerevisiae is a multi-subunit membrane protein that facilitates the acidification of intracellular compartments. I am particularly interested in the overall architecture of this enzyme, how it assembles and interacts with other components of the cell, as well as how it functions. Since this membrane bound, macromolecular machine is very large it poses numerous challenges to the experimental investigation. The recently obtained structure of the regulatory subunit H of this enzyme provides a first glimpse into the architecture. Since the malfunction of this protein causes severe diseases in eucaryotes we hope that future investigations of this enzyme will contribute to the understanding of disease prevention.

2) To this day protein folding and protein stability remain poorly understood phenomena. The de novo design of proteins is still a very challenging endeavor and the redesign of natural proteins appears to be a more promising approach to engineer new architectures and functions into proteins. The principle goal is to derive basic principles that permit the integration of structural and functional protein fragments into new host proteins. Using substitution and insertion experiments we deliberately alter the code of a protein sequence to gain understanding in the folding process.

In particular, we seek to understand to what degree secondary structure formation is determined by the local, structural environment. To test context driven structure formation, we "copy and paste" elements of secondary structure into different locations of a host protein. By using this method we have found, for example, that even highly conserved structures do not necessarily exhibit high folding propensity.

Furthermore, the copy-and-paste methodology of secondary structures into proteins has enabled us to artificially engineer "nano-switches" into proteins. Specifically, with the insertion of tandem sequence repeats into a host protein it is possible to generate alternatively folded protein structures. Crystallographic characterizations of these structures have revealed key interactions that specifically stabilize a single conformational state. With the deletion of only a few key interactions by site-directed mutagenesis it is possible to induce a large-scale structural interconversion within the protein(*). The above-shown animation shows a possible dynamics model of such an engineered helix switch. The red and the yellow structures highlight the sequence copies of the tandem repeat. The calculations are based on the individual crystal structures using simplified normal-mode dynamics calculations. We hypothesize that similar switches can also be introduced into other proteins.

The design and engineering of the described structural nano-switches is unprecedented and has not yet been observed in natural proteins. Our research in nano-mechanics is designed to develop an understanding on structural interconversions and structural dynamics of proteins and to establish methodology for the engineering of novel responsive materials and devices.

(* Trends Biotech, 2004,22,1-2; PNAS, 2004, 101, 11583-6)