Abstract Werner Kühlbrandt
High-resolution cryoEM of membrane protein complexes
Werner Kühlbrandt
Max Planck Institute of Biophysics,
Department of Structural Biology, Max-von-Laue Str. 3, 60438 Frankfurt am Main,
Germany
With the ongoing resolution revolution in electron cryo-microscopy (cryoEM), large and dynamic membrane protein complexes that were intractable for decades have become accessible to high-resolution structural studies. Cryo-EM of non-crystalline samples at near-atomic resolution resolves sidechains, bound cofactors, lipids, ions and water molecules. As an added bonus, cryoEM delivers images of co-existing conformational states. Images of different conformations are separated by image processing. The same microscopes and detectors are used to image macromolecular assemblies in their cellular or organellar context by electron tomography, at increasingly high resolution.
After a brief introduction to the method, the lecture will describe cryo-EM structures of the soluble Frh complex at ~2 Å resolution. Current technical limitations will be discussed. The recent high-resolution cryo-EM structures of intact chloroplast ATP synthase reveals how it is turned off at night to prevent unproductive ATP hydrolysis. In the mitochondrial ATP synthase dimer of Polytomella, thirteen different rotary substates with three primary rotary states provide unexpected insights into the universal mechanism of ATP synthesis. The membrane portions of both the chloroplast and mitochondrial ATP synthase indicate two aqueous channels that have been conserved over an evolutionary distance of around 1.5 billion years. The channels conduct protons to and from the rotor that drives ATP production, as in a turbine. Electron tomography indicates that the chloroplast ATP synthase is monomeric, whereas all mitochondrial ATP synthases form dimers that assemble into long rows. Mechanistic implications will be discussed.