Seminar

Prof. Dr. Werner Kühlbrandt

Director, Department of Structural Biology

Max-Planck-Institut für Biophysik, Max-von-Laue-Str.3

D-60438 Frankfurt am Main, Germany

http://www.mpibp-frankfurt.mpg.de/structuralbiology/

Towards a corrected phase-contrast electron microscope for structural biology

Friday, May 25th, 2007, 2:00 pm

1022 Life Sciences (LSA)

Electron microscopy has great potential for determining the structures of biological macromolecules at high to intermediate resolution. Three main techniques are of interest for biological systems: electron tomography of whole cells or membranes, single-particle cryo-EM of large protein complexes suspended in vitrified water, and electron crystallography of two-dimensional (2D) crystals on thin support films. Examples of all three will be shown. However, all present applications to biological specimens suffer from low contrast, since the objects of interest, as well as the media surrounding them, consist primarily of light atoms that modify the phase of the scattered electron wave only weakly.

Currently, low-resolution contrast in biological cryo-EM is generated by defocusing the objective lens, but this procedure severely degrades the high-resolution information. Higher contrast at both high and low special frequencies can be achieved by an electrostatic quarter wave plate, which shifts the phase of the unscattered electron wave by 90°. In order to be useful in practice, the Boersch phase plate needs to be combined with a transfer lens that magnifies the back focal plane of the objective lens so as to minimize loss of low-resolution information. Optimally, it should be combined with a chromatic aberration corrector. We are exploring a new design of an electrostatic phase plate that avoids obstruction of any part of the beam path and should thus be optimally useful for a wide range of EM applications.

Contact: Henning Stahlberg, MCB, CBS. HStahlberg@ucdavis.edu, (530) 752 8282, http://stahlberglab.ucdavis.edu