The Harvard Center for Cryo-Electron Microscopy (HC2EM) is a joint effort by Harvard Medical School, Dana-Farber Cancer Institute, Boston Children’s Hospital, and Massachusetts General Hospital to provide state-of-the-art cryo-EM instrumentation and expertise for the Harvard structural biology community. This user facility offers consultation and training by staff in specimen preparation, microscope operation, image acquisition, and data analysis. 

Additionally, the Molecular Electron Microscopy Suite (MEMS) at Harvard Medical School is a separate user resource currently available to qualified researchers. This user facility offers training and supervision in negative-stain and cryo-transmission electron microscopy. Equipment includes three transmission electron microscopes, two cryo plungers, and sample preparation areas. 

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Recent Publications

Alex G. Johnson, Tanita Wein, Megan L. Mayer, Brianna Duncan-Lowey, Erez Yirmiya, Yaara Oppenheimer-Shaanan, Gil Amitai, Rotem Sorek, and Philip J. Kranzusch. 2022. “Bacterial gasdermins reveal an ancient mechanism of cell death.” Science, 375, 6577, Pp. 221-225. Publisher's VersionAbstract
Gasdermins are cell death proteins in mammals that form membrane pores in response to pathogen infection. Johnson et al. report that diverse bacteria encode structural and functional homologs of mammalian gasdermins. Like their mammalian counterparts, bacterial gasdermins are activated by caspase-like proteases, oligomerize into large membrane pores, and defend against pathogen—in this case, bacteriophage—infection. Proteolytic activation occurs through the release of a short inhibitory peptide, and many bacterial gasdermins are lipidated to facilitate membrane pore formation. Pyroptotic cell death, a central component of mammalian innate immunity, thus has a shared origin with an ancient antibacteriophage defense system. —SMH Bacteria encode gasdermins that are activated by dedicated proteases, defend from phage, and induce cell death. Gasdermin proteins form large membrane pores in human cells that release immune cytokines and induce lytic cell death. Gasdermin pore formation is triggered by caspase-mediated cleavage during inflammasome signaling and is critical for defense against pathogens and cancer. We discovered gasdermin homologs encoded in bacteria that defended against phages and executed cell death. Structures of bacterial gasdermins revealed a conserved pore-forming domain that was stabilized in the inactive state with a buried lipid modification. Bacterial gasdermins were activated by dedicated caspase-like proteases that catalyzed site-specific cleavage and the removal of an inhibitory C-terminal peptide. Release of autoinhibition induced the assembly of large and heterogeneous pores that disrupted membrane integrity. Thus, pyroptosis is an ancient form of regulated cell death shared between bacteria and animals.
Haixia Zhou, Manal S Zaher, Johannes C Walter, and Alan Brown. 12/1/2021. “Structure of CRL2Lrr1, the E3 ubiquitin ligase that promotes DNA replication termination in vertebrates.” Nucleic Acids Research. Publisher's VersionAbstract
When vertebrate replisomes from neighboring origins converge, the Mcm7 subunit of the replicative helicase, CMG, is ubiquitylated by the E3 ubiquitin ligase, CRL2Lrr1. Polyubiquitylated CMG is then disassembled by the p97 ATPase, leading to replication termination. To avoid premature replisome disassembly, CRL2Lrr1 is only recruited to CMGs after they converge, but the underlying mechanism is unclear. Here, we use cryogenic electron microscopy to determine structures of recombinant Xenopus laevis CRL2Lrr1 with and without neddylation. The structures reveal that CRL2Lrr1 adopts an unusually open architecture, in which the putative substrate-recognition subunit, Lrr1, is located far from the catalytic module that catalyzes ubiquitin transfer. We further demonstrate that a predicted, flexible pleckstrin homology domain at the N-terminus of Lrr1 is essential to target CRL2Lrr1 to terminated CMGs. We propose a hypothetical model that explains how CRL2Lrr1’s catalytic module is positioned next to the ubiquitylation site on Mcm7, and why CRL2Lrr1 binds CMG only after replisomes converge.
Katherine G. Nabel, Sarah A. Clark, Sundaresh Shankar, Junhua Pan, Lars E. Clark, Pan Yang, Adrian Coscia, Lindsay G. A. McKay, Haley H. Varnum, Vesna Brusic, Nicole V. Tolan, Guohai Zhou, Michaël Desjardins, Sarah E. Turbett, Sanjat Kanjilal, Amy C. Sherman, Anand Dighe, Regina C. LaRocque, Edward T. Ryan, Casey Tylek, Joel F. Cohen-Solal, Anhdao T. Darcy, Davide Tavella, Anca Clabbers, Yao Fan, Anthony Griffiths, Ivan R. Correia, Jane Seagal, Lindsey R. Baden, Richelle C. Charles, and Jonathan Abraham. 12/2/2021. “Structural basis for continued antibody evasion by the SARS-CoV-2 receptor binding domain.” Science, Pp. eabl6251.Abstract
Many studies have examined the impact of SARS-CoV-2 variants on neutralizing antibody activity after they have become dominant strains. Here, we evaluate the consequences of further viral evolution. We demonstrate mechanisms through which the SARS-CoV-2 receptor binding domain (RBD) can tolerate large numbers of simultaneous antibody escape mutations and show that pseudotypes containing up to seven mutations, as opposed to the one to three found in previously studied variants of concern, are more resistant to neutralization by therapeutic antibodies and serum from vaccine recipients. We identify an antibody that binds the RBD core to neutralize pseudotypes for all tested variants but show that the RBD can acquire an N-linked glycan to escape neutralization. Our findings portend continued emergence of escape variants as SARS-CoV-2 adapts to humans.

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A Better Look: The development of cryo-EM has revolutionized structural biology

September 12, 2018
"Throughout history, observations of structure, from Hooke’s cells to the beaks of Darwin’s finches, have provided insights necessary to understand how life works. This is particularly true in structural biology, a discipline focused on visualizing life at its most fundamental. Discoveries of the atomic structures of important proteins and biological molecules have been among the most celebrated in science and have generated more than a dozen Nobel Prizes, new fields of research, and multibillion-dollar companies."

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