Prof. Carsten Sachse, Forschungszentrum Jülich

Single-particle cryo-EM of isolated and purified protein complexes using has become a highly successful method of structure determination in the last decade. At the Ernst Ruska Centre, we advance electron microscopy methods to visualize biological core mechanisms at high resolution and I will give an overview of ongoing technological developments and activities. I will showcase our efforts in understanding the membrane remodeling of ESCRT complexes in bacteria using single-particle cryo-EM. Critical to these processes is the assembly of ESCRT-III subunits into polymeric structures. Recently, we determined the 3.6 Å resolution cryo-EM structure of bacterial PspA assembled in helical rods. PspA, the main effector of the phage shock protein (Psp) response, preserves the integrity and functions of the bacterial inner membrane. PspA rods are variable in diameter and capable of enclosing lipids and generate positive membrane curvature. Using cryo-EM, we visualized how the plasticity of PspA rods is critical for remodeling membrane vesicles into μm-sized structures and how it mediates the formation of internalized vesicular structures. Moreover, I will present structural insights of the cell biological process of autophagy. First, we resolved the high-resolution structure of selective autophagy receptor p62/SQSTM1. At the same time, we provide the cellular context of early stages of lipid droplet cargo enwrapping mediated by p62. Second, we observed one of the mechanisms of how the phagophore extends in size to encapsulate cargo. Together, the results show that a combination of novel technologies and targeted cell biological tools can reveal fundamental structural insights into the process of the ESCRT machinery and autophagy.