Many chemical and biological processes take place in a non-crystalline environment or concern molecules with reduced molecular mobility. Important examples include polymers, protein aggregates or membrane proteins. These systems are intimately related to questions such as: - How is information transmitted across the cellular membrane? - Which factors impede correct protein folding? - How does a fuel cell work? Magnetic Resonance in the solid-state (solid-state NMR) is a tool to answer such questions on the molecular level. Progress in solid-state NMR methodology, instrumentation and sample preparation permit us to study molecular structure and dynamics with increasing accuracy and flexibility. Solid-state NMR is increasingly used in physical chemistry, biophysics and structural biology. Our studies often involve the combined application of solid-state NMR and other biophysical methods and can find direct application in research areas such as nanotechnology or pharmacology.
Increasing evidence suggests that biological functioning is controlled by biomolecular interaction networks, often in a heterogeneous and dense molecular environment. For example, the cellular response to outside stimuli such as light or nutrients or the process of protein aggregation in the context of Alzheimers disease are taking place in a more complex and dense cellular environment than previously envisioned.
Solid-state Nuclear Magnetic Resonance (ssNMR) offers novel possibilities to address such systems on the molecular level since sample crystallinity or solubility is not required and experiments can be conducted under different preparatory conditions including powders, frozen solutions, precipitants, gels or proteoliposomes (Figure). SsNMR hence represents a versatile spectroscopic technique to study challenging biomolecular systems in a functional setting.
We develop and apply high-resolution solid-state NMR methods to study 3D molecular structure and dynamics in complex biological molecules in close relationship to function. For a review, see for example, M. Baldus, J. Biomol. NMR (2007).
Such techniques can be used to understand the function of a potassium ion channel, a membrane-embedded protein that controls the ion flow across the cell membrane, on the atomic level (See Figure). Firstly, proteins are reconstituted in lipid bilayers and then ssNMR experiments are performed to study the structure and dynamics of the protein in different functional states on the atomic level.
For example, two-dimensional ssNMR spectra (Figure) were recorded to study the binding of a toxin to the channel (Lange et al., Nature 2006). More recently, we followed the structural changes that occurr after inactivation of the channel in a membrane environment (Ader, Schneider et al., Nature Struct. Mol. Bio. 2008) and the coupling of activation and inactivation gates (Ader, Schneider et al., EMBO J 2009).
In addition, such ssNMR methods can be used to study molecular structures in other membrane-embedded proteins including G-protein coupled receptors (Luca et al., PNAS 2003), photoreceptors (Etzkorn et al., Angew. Chemie 2007, Etzkorn et al., Structure 2010), Enzymes (Seidel et al., Biochemistry 2008) and Histidine kinases (Etzkorn et al., Nature Struct. Mol. Bio. 2008).
In parallel, we also have been using ssNMR to study protein folding and aggregation. For example, we have studied the fibrillar and prefibrillar states of alpha-synuclein involved in Parkison's disease (Heise et al., PNAS 2005, Karpinar et al., EMBO J 2009) and we examined the structure of paired helical filaments formed by a construct related to tau protein (Andronesi et al., JACS 2008). We also revealed a new paradigm that elucidates the structural and dynamical organization of nuclear pore proteins and provides a direct link to Amyloid disease states (Ader, Frey et al., PNAS 2010) . Most recently, ssNMR also revealed that protein refolding is required for assembly of the type
three secretion needle (Poyraz, Schmidt, Seidel et al., Nature Struct.Mol.Bio. 2010, in press).
In addition, ssNMR also provides exciting possibilities to study structure and workings of novel (bio)materials. For example, we have used ssNMR to examine the working of hydrogen fuel cells (Hughes et al., JCP 2004) or the structure of organicmetallic compounds (Ganapathi et al., Angew. Chemie 2003).