Webinar

Liquid phase electron microscopy, fundamentals, application to study membrane proteins in whole cells, and future outlook

Presenter:

Prof. Dr. Dr. h.c. Niels de Jonge
Website: http://home/denssolutions/public_html.dejonge.physik.uni-saarland.de
INM – Leibniz Institute for New Materials, Saarbrücken, Germany
Physics Department, Saarland University, Saarbrücken, Germany

Abstract:

Transmission electron microscopy (TEM) has traditionally been associated with the study of thin solid samples in vacuum. With the availability of reliable thin membranes of silicon nitride, TEM of liquid specimens has become accessible with nanoscale resolution in the past decade with a wide range of applications in materials science, chemistry, and biological research (1).

The usage of scanning transmission electron microscopy (STEM) presents a novel concept to study cells in their native liquid environment (2). The cells in liquid are placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are then imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For many studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector (3). A third option is to cover a liquid specimen under a thin membrane of graphene providing the thinnest possible layer (4). The obtained spatial resolution is typically limited by ration damage (5) but is enhanced by an order of magnitude in liquid compared to samples in ice (6).

Liquid-phase STEM was used to explore the formation of HER2 homodimers at the single-molecule level in intact SKBR3 breast cancer cells in liquid state (3). HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Data analysis based on calculating the pair correlation function from individual HER2 positions revealed remarkable differences in its functional state between rare- and bulk cancer cells with relevance for studying the role of cancer cell heterogeneity in drug response. We discovered a small sub-populations of cancer cells with a different response to a prescription drug (7).

The full scale application of LP-EM for soft matter research still faces several challenges but strategies to overcome them are emerging, so that time-resolved LP-EM of biomolecular processes is within reach (8).   

References

1. N. de Jonge, F. M. Ross, Electron microscopy of specimens in liquid. Nat. Nanotechnol. 6, 695-704 (2011).
2. N. de Jonge, D. B. Peckys, G. J. Kremers, D. W. Piston, Electron microscopy of whole cells in liquid with nanometer resolution. Proc. Natl. Acad. Sci. 106, 2159-2164 (2009).
3. D. B. Peckys, U. Korf, N. de Jonge, Local variations of HER2 dimerization in breast cancer cells discovered by correlative fluorescence and liquid electron microscopy. Sci. Adv. 1, e1500165 (2015).
4. I. N. Dahmke et al., Graphene Liquid Enclosure for Single-Molecule Analysis of Membrane Proteins in Whole Cells Using Electron Microscopy. ACS Nano 11, 11108-11117 (2017).
5. N. de Jonge, L. Houben, R. E. Dunin-Borkowski, F. M. Ross, Resolution and aberration correction in liquid cell transmission electron microscopy. Nat. Rev. Mater. 4, 61-78 (2019).
6. S. Keskin, N. de Jonge, Reduced radiation damage in transmission electron microscopy of proteins in graphene liquid cells. Nano Lett. 18, 7435-7440 (2018).
7. D. B. Peckys, U. Korf, S. Wiemann, N. de Jonge, Liquid-phase electron microscopy of molecular drug response in breast cancer cells reveals irresponsive cell subpopulations related to lack of HER2 homodimers. Mol. Biol. Cell 28, 3193-3202 (2017).
8. H. Wu, H. Friedrich, J. P. Patterson, N. Sommerdijk, N. de Jonge, Liquid-Phase Electron Microscopy for Soft Matter Science and Biology. Adv Mater 10.1002/adma.202001582, e2001582 (2020).