There is a scarcity of structures in the Protein Data Bank (PDB) corresponding to integral membrane proteins, higher order eukaryotic proteins, and large protein complexes. Given the pertinence of these classes of proteins to human health, it is clear that novel approaches are still urgently needed to address the challenges posed by these macromolecules that are often related to instability, low yields, and the need to visualize transient complexes. Transmission electron microscopy (TEM) has a role to play in accelerating structure determination in three areas: X-ray crystallography, Electron Crystallography and Single Particle EM (SPEM), but is hampered by low throughput and the sample volume requirements. We proposed to develop a novel approach to TEM specimen preparation, incorporating miniaturization and small volume (picoliter to nanoliter) dispensing that will enable TEM to be integrated seamlessly into the flow of existing high-throughput structural biology efforts. Compared to currently available methodology, our approach dramatically reduces the amount of protein required (1000x) and significantly enhances the overall throughput of TEM sample preparation and imaging (100x). In preliminary work, we have demonstrated that inkjet technology can be utilized to dispense picoliter to nanoliter volumes of reagents with high spatial precision and specimens can be confined to micro- scale regions on a single grid in a defined pattern. We also verified that inkjet dispensing does not disrupt the structure of macromolecules.
In specific aim 1, we will develop and test inkjet instrumentation for small volume transfer of specimens from 96-well plates to targeted micro-scale regions on a single EM grid.
In specific aim 2, we will use microwell array technology to fabricate novel EM grid substrates capable of segregating ~96 independent samples and incorporate novel materials to provide highly controlled local blotting around each microwell.
In specific aim 3, we will integrat these novel EM grids into an automated multi-scale TEM imaging pipeline and test and validate the methods using driving biological projects that are focused on solving structures of integral membrane proteins, low-yield eukaryotic complexes, and transient multi-unit protein assemblies. Members of our team provide the multi-disciplinary experience and skills (instrumentation and microfabrication, structural biology, automated TEM) required to accomplish all aspects of this project. We have strong support from members of the PSI: Biology Network who are enthusiastically supportive of the potential for using an HT-TEM platform to accelerate structure determination of challenging macromolecular systems.
There is a critical need for further structural understanding of integral membrane proteins, higher order eukaryotic proteins, and large protein complexes, given the importance of these classes of proteins to human health. We will develop a novel high-throughput Transmission Electron Microscopy pipeline that will accelerate structure determination in three areas: X-ray crystallography, Electron Crystallography and Single Particle Electron Miroscopy.