Single-particle cryo-electron microscopy of the machinery involved in abnormal protein aggregation
Three-dimensional image reconstruction of an Alzheimer’s Aβ(1-40) fibril superimposed on an electron micrograph.
High-resolution helical reconstruction of tobacco mosaic virus at near-atomic resolution using single-particle cryo-EM. Top: helical rod. Center: cross section. Bottom: close-up of side-chain density.
The Sachse group uses cryo-electron microscopy to study protein aggregates, typical of neurodegerative diseases such as Alzheimer’s, and the mechanisms cells normally use to eliminate them.
Previous and current research
The molecular hallmark of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, is the formation of large protein aggregates called amyloid fibrils. The net build-up of these fibrillar aggregates is a result of an imbalance in the cellular production and clearance of misfolded polypeptides. In our group, we are investigating the molecular structures involved in these aberrant processes as they provide fundamental insights in our understanding of ageing and neuronal dysfunction.
We are visualising the molecules by cryo-electron microscopy (cryo-EM), because large macromolecular structures and multi-protein complexes can be studied in their near-native environment without the need for crystals. Small amounts of material are sufficient to obtain ‘snapshots’ of single particles in the cryo-electron microscope and subsequent computer-aided image processing enables 3D image reconstruction. To realise the promising potential of the technique, the scientific community is still in great need of hardware-based improvements and software enhancements. Therefore, we are also interested in developing techniques, including sample preparation and data processing, to ultimately increase the resolution of single-particle cryo-EM. We would like to make it a routine tool for structural biology research of large macromolecules.
Future projects and goals
Autophagy (from Greek, meaning ‘to eat oneself’) is the cell’s housekeeping mechanism to engulf and degrade large protein aggregates, damaged organelles and even microbes in double-membrane vesicles called autophagosomes. Multiprotein complexes are essential mediators in the events leading to autophagy. On the structural level, little is known about their 3D architecture and thus fundamental questions on the nature of these complexes need to be addressed:
- How are protein deposits structurally linked to autophagy?
- What are the shapes of these multiprotein assemblies at the membrane?
- How do they give rise to the cellular structure of the autophagosome?
Spring is a single-particle based helical reconstruction package and has been used to determine 3D structures of a variety of highly ordered and less ordered specimens from electron micrographs.