Electron Microscopy of Selected Proteins and Protein Complexes Through Preparative Mass Spectrometry

In order to take a picture of a large biological molecule, such as a protein, it has to be frozen in a very thin sheet of ice where it can be imaged by an electron microscope.
Many images of the same type of molecule are laid over another to improve the resolution, ultimately revealing atomic positions. This procedure requires a highly pure protein sample in solution and plunge freezing of water films hanging in very fine mesh grids, a procedure which is not compatible with all proteins. In particular proteins that reside in cell membranes, prefer to be at the water-air surface, where they are destroyed and thus cannot be imaged. Also protein, which are composed from many subunits cannot be purified sufficiently so that the averaging will fail produce a high resolution image.

This proposal aims at developing an alternative sample preparation method, based on native electrospray mass spectrometry. Native electrospray ionisation can transfer a protein from solution into a gaseous particle with charge, which can be weighed (by mass spectrometry) and hence chemically identified. We will use this process to isolate the particle and instead of only detecting it, we will enrich one selected type of protein on the sample for electron microscopy. The major challenge thereby is to land the molecule so gentle, that it's characteristic native shape is not destroyed in the process. With mass-selected sample fabrication we can link chemical information to protein structure, which is information highly desirable in the development of medicine and biology.