Biochemistry | Molecular Biology | Structural Biology |Enzymology
Biological membranes contain a variety of proteins, which fulfill different crucial cellular functions, ranging from cell signaling to ion transport. Moreover, membrane proteins are associated with different human diseases such as cystic fibrosis and Alzheimer’s. It is therefore not surprising that these proteins comprise important drug targets. In fact, membrane proteins are the largest class of targets for FDA-approved drugs. Typically, membrane proteins are inserted into the membrane and these are known as integral membrane proteins. Integral membrane proteins are anchored into the membrane by transmembrane alpha-helices made up of stretches of about twenty hydrophobic amino acids. About 25% of a typical proteome comprises alpha-helical membrane proteins.
Similar to other proteins, integral membrane proteins are synthesized by ribosomes in the cytoplasm. However, these proteins are prone to aggregation due to their hydrophobic transmembrane domains. To prevent this, ribosomes that produce integral membrane proteins are transported to the membrane during protein synthesis in a process which is known as co-translational targeting. Different targeting and insertion factors as well as various folding catalysts ensure that newly synthesized membrane proteins end up safely into the membrane and fold into their biologically active conformation, while dedicated proteases remove misfolded membrane proteins, thereby preventing their toxic accumulation. I am particularly interested in the structure and mechanism of different molecular factors that target, fold and assemble newly synthesized membrane proteins.
Many proteins function at other places than the cytoplasm such as in different organelles, biological membranes or extracellular space. These proteins are, however, synthesized by cytosolic ribosomes and are subsequently transported out of the cytoplasm to their place of action. How is this logistical feat actually accomplished? Proteins that are transported out of the cytoplasm are typically synthesized with an N-terminal signal peptide. This signal peptide functions as a molecular export signal and directs the protein to its final destination across a membrane into an organelle or extracellular space. This signal peptide is recognized by a dedicated import apparatus located in the target membrane, which facilitates its membrane translocation. Moreover, protein translocation pathways have emerged as attractive targets for anticancer drugs. I am particularly interested in the structure and mechanism of eukaryotic and bacterial import/export machineries that facilitate the translocation of proteins across membranes as well as their biotechnological application.
Pioneering biochemical experiments established that in a test tube unfolded proteins are able to refold into their functional conformation without any assistance, indicating that their primary sequence contains all the information that is required for proper folding. However, this is not the case inside a cell because here every step of the folding process is assisted by different molecular factors known as folding catalysts and chaperones. The importance of properly folded proteins is emphasized by the toxic accumulation of misfolded proteins, resulting in different devastating neurodegenerative pathologies such as Alzheimer’s and Huntington’s. To ensure that a protein is properly folded, different folding catalysts already associate with the protein early during its production and promote the first folding steps, while the later and often more complex folding events are catalyzed by dedicated molecular chaperones. I am particularly interested in the structure and mechanism of bacterial folding catalysts and chaperones as well as their application in heterologous protein production.
Enzymes are Nature’s own catalyst speeding up biochemical reactions. Nearly all biological processes depend one or more dedicated enzymes, ranging from metabolism to host-defense responses and cell division. In fact, without enzymes life would be impossible. Many enzymes require additional molecules, such as metal ions and organic molecules, for full functionality. These are known as cofactor or coenzyme and important examples include zinc and metal ions as well as riboflavin, NADH, NADPH and coenzyme A. Importantly, enzymes typically operate under mild reaction conditions (ambient temperature and atmospheric pressure) and use cheap cosubstrates (e.g. oxygen). Moreover, enzyme-catalyzed reactions often display outstanding selectivity and good yield, which are difficult to achieve by chemical means. These features ensure that enzymes are also industrially relevant. Many studies demonstrate the use of enzymes as alternatives for the production of fine chemicals. I am particularly interested in the structure and mechanism of enzymes as well as their biotechnological application (biocatalysis).