From high-resolution AFM topographs to atomic models of supramolecular assemblies

Atomic force microscopy (AFM) has developed into a powerful tool in membrane biology. AFM features an outstanding signal-to-noise ratio that allows substructures on individual macromolecules to be visualized. Most recently, AFM topographs have shown the supramolecular assembly of the bacterial photosynthetic complexes in native membranes. Here, we have determined the translational and rotational degrees of freedom of the complexes in AFM images of multi-protein assemblies, in order to build realistic atomic models of supramolecular assemblies by docking high-resolution structures into the topographs. Membrane protein assemblies of megadalton size comprising several hundreds of polypeptide chains and pigments were built with Angstrom precision.