Membrane Proteins

In our group, a major focus lies on membrane proteins. Distinct from other methods in structural biology, solid-state NMR makes it possible to study membrane proteins in native-like lipid bilayers at room temperature and under physiological buffer conditions. Current projects involve for instance non-selective cation channels such as NaK that are able to conduct both sodium (Na+) and potassium (K+) with equally high efficiency (see Figure). In contrast to previous crystallographic results, we could recently show that the selectivity filter of NaK in native-like lipid membranes adopts two distinct conformations that are stabilized by either Na+ or K+ ions. The atomic differences of these conformations were resolved by solid-state NMR spectroscopy and molecular dynamics (MD) simulations. We propose that structural plasticity within the selectivity filter and the selection of these conformations by different ions are key molecular determinants for highly efficient conduction of different ions in non-selective cation channels (Shi et al., Nature Communications 2018). In a related study on the selective K+ channel NaK2K, we showed that the selectivity filter is entirely occupied by K+ ions, and not - as previously thought - alternatingly occupied by water and K+ (Öster er al., Science Advances 2019). Other membrane proteins of interest comprise the human voltage-dependent anion channel (VDAC) (Schneider et al., Angewandte Chemie 2010; Zachariae et al., Structure 2012), the histidine kinase CitA (Salvi et al., PNAS 2017), and rhomboid proteases, that initiate signal cascades by cleaving proteins within the membrane and thus releasing signal proteins that are no longer anchored. Recently, we have performed a thorough structural and dynamic characterization of the rhomboid protease GlpG in liposomes. In this context we characterized the dynamic process responsible for opening and closing of the gating helix that allows the substrate to enter the active site (Shi et al., JACS 2019). More recently, we studied inhibitor binding using a combination of solid-state NMR, biochemical assays and MD simulations (Bohg et al., Chemical Science 2021). In this study we investigated hydrogen/deuterium exchange to identify residues that are protected from exposure to water due to inhibitor binding. We also identified allosteric effects and structural dynamics caused by inhibitor binding. By combining these solid-state NMR results with docking and molecular dynamics simulations, we were able to characterize the binding mode of an inhibitor.