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Research

Nuclear Magnetic Resonance (NMR) spectroscopy is based on the interaction of nuclear magnetic momenta with an external magnetic field and the readout of resonance frequencies, lifetimes of non-equilibrium states, and spatial spin proximities. Employing such principles, the technique is capable of assessing molecular structure and dynamics with of atomic resolution. This can be applied to proteins: Soluble proteins can be characterized using a huge set of established solution NMR methodology. On the other hand, solid-state NMR is applied for example to study membrane proteins in a lipid-bilayer setting or amyloidogenic proteins. This approach has witnessed significant developments in the strategies employed in the last years. One such development is the availability of proton detection rather than detection of heteronuclear signals, which has been drivin by the development of equipment that allow fast Magic-Angle Spinning (MAS) of the sample (on the order of 100 000 rotations per second) in the magnetic field.

Our group focuses on various aspects of NMR spectroscopy, both in terms of methods development as well as application to gain understanding of biology-related questions. As such, we strive for methods enabling structure elucidation of proteins with increasing molecular size or which are characterized by significant sample heterogeneity or limitations in isotope-labeled protein expression. This concerns the structure of such proteins as well as the dynamics relevant for protein functionality. We develop dedicated isotope labeling schemes in conjunction with new spectroscopic approaches as building blocks of our spectroscopic pulse schemes. Based on the developed methodology, we are in the position to give answers to questions about the details of specific proteins’ structure and dynamics, protein-water interactions, protein-ligand interactions, ligand mobility and chemical mechanisms comprised in the active site.

In the past, we have focused on proteins fibrils, as they occur in the course of many neurodegenerative diseases, on membrane proteins, and on enzymes. Both, strategies newly developed by us, like for protein labeling and expression techniques or for fast-MAS-based characterization of proteins, as well as established approaches have been made use of extensively, both in the course of solution NMR and in the solid state.

Apart from its use for proteins, both solid-state and solution-state NMR represent tools for the elucidation of small molecule configuration, conformations, dynamics, exchange, and interactions. Solid-state NMR provides detailed information on chemical bond parameters like asymmetry as well as distances, which can be used successfully for characterization of such molecules that are different from their soluble counterparts, like polymers, grafted catalysts, and molecules interacting with lipid membranes or inorganic gels.

Exemplary research directions:

Figure 1: The amyoidogenic hydrophobin EAS (solution structure of the monomer in A), forming water-repellant layers on fungal spores, as seen by EM (B) and by solid-state NMR at 60 kHz MAS (C), together with a preliminary structural model (D).

Figure 2: 4D diagonal-free HNNH correlations of the micro-crystalline SH3 domain of chicken a-spectrin (A), the nature of the obtained restraints (B), and the structural picture obtained from sparse but highest-quality structural restraints (C).

Figure 3: Protein fibrils, as they are formed by amyloidogenic proteins like the tau protein and in the course of many neurodegenerative diseases, are a primary class of proteins amenable to solid-state NMR.

Figure 4: Protein dynamics are often key to understanding the details of protein functionality. This transmembrane domain of the transcriptional activator SREBP1 comprises a flexing enabled by a conserved amino acid motif, which enables conformations dependent on the surrounding lipids.

Figure 5: Solid-state-NMR-derived characterization of inorganic compounds. Left: Proton-proton DQ-SQ through-space correlations of an Ir-complex at 60 kHz MAS (in collaboration with Prof. Dr. Barbara Messerle). Right: Elucidation of bonding electron distributions in a silylone compound (together with Prof. Dr. Herbert W. Roesky).