Method developments for high resolution transmission electron microscopy

The technical platform for cryoEM in Flemingsberg, affiliated both with The Royal Institute of Technology and Karolinska Institutet, serves as a regional infrastructure which allows state of the art structural studies of biological specimens. Recent technical developments, in particular with regard to the advances of new direct electron detectors, amounts to a quantum leap of capability. It is now feasible to determine structures from EM data at resolution levels which allow building of atomic models without prior crystallization, a step that is often a bottle neck for X-ray diffraction studies. A direct electron detector has recently been installed on one of our electron microscopes.

The specimens to be studied, individual macromolecules or larger complexes, often display heterogeneity likely connected to their functions. Applications of cryoEM give unique opportunities to study molecular flexibility. However, such studies put considerable demands with regard to processing and being able to collect very large data sets. We are addressing both of these hurdles by developing new algorithms and by implementing high throughput methods.

Even if electron crystallography can be used to determine the structures of membrane proteins at near-atomic resolution many projects remain at a resolution around 10 Å. This might be partly due to lack of flatness of two-dimensional crystals. We have investigated this problem and suggest single particle processing of locally averaged unit cells to improve the quality and possibly the resolution of three-dimensional maps.

Contact persons: Docent Philip Koeck, Docent Martin Lindahl

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