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Highlights of Coronavirus Structural Studies

Coronavirus Archive

Research Highlights

the best of science obtained using CIISB Core Facilities

Current Biology 2022

The catalytic center of [FeFe] hydrogenases, in which the molecular hydrogen oxidation or synthesis takes place, is called the H-cluster. It is a highly complex metallo-organic structure that is composed of a canonical [4Fe4S] cubane-cluster that, through a cysteine residue, binds a unique [FeFe] subcluster, which is coordinated with three CO, two CN, and one unusual azadithiolate bridging ligand.

Jan Tachezy Research Group


Trichomonads, represented by the highly prevalent sexually transmitted human parasite Trichomonas vaginalis, are anaerobic eukaryotes with hydrogenosomes in the place of the standard mitochondria. Hydrogenosomes form indispensable FeS-clusters, synthesize ATP, and release molecular hydrogen as a waste product. Hydrogen formation is catalyzed by [FeFe] hydrogenase, the hallmark enzyme of all hydrogenosomes found in various eukaryotic anaerobes. Eukaryotic hydrogenases were originally thought to be exclusively localized within organelles, but today few eukaryotic anaerobes are known that possess hydrogenase in their cytosol. We identified a thus-far unknown hydrogenase in T. vaginalis cytosol that cannot use ferredoxin as a redox partner but can use cytochrome b5 as an electron acceptor. Trichomonads overexpressing the cytosolic hydrogenase, while maintaining the carbon flux through hydrogenosomes, show decreased excretion of hydrogen and increased excretion of methylated alcohols, suggesting that the cytosolic hydrogenase uses the hydrogen gas as a source of reducing power for the reactions occurring in the cytoplasm and thus accounts for the overall redox balance. This is the first evidence of hydrogen uptake in a eukaryote, although further work is needed to confirm it. Assembly of the catalytic center of [FeFe] hydrogenases (H-cluster) requires the activity of three dedicated maturases, and these proteins in T. vaginalis are exclusively localized in hydrogenosomes, where they participate in the maturation of organellar hydrogenases. Despite the different subcellular localization of cytosolic hydrogenase and maturases, the H-cluster is present in the cytosolic enzyme, suggesting the existence of an alternative mechanism of H-cluster assembly.


Smutna, T. ; Dohnalkova, A. ; Sutak, R. ; Narayanasamy, R.K.; Tachezy, J., and Hrdy, I.: A cytosolic ferredoxin-independent hydrogenase possibly mediates hydrogen uptake in Trichomonas vaginalis, Current Biol. 2022, 32, R49-R51,

EMBO Journal 2022

Cryo-EM structures of CspA27 inside the exit tunnel

  1. Structure and nascent chain contacts in the exit tunnel for CspA27-1.
  2. Structure and nascent chain contacts in the exit tunnel for CspA27-2.
  3. Structure and nascent chain contacts in the exit tunnel for CspA27-3.

Marina V. Rodnina Research Group


Cellular proteins begin to fold as they emerge from the ribosome. The folding landscape of nascent chains is not only shaped by their amino acid sequence but also by the interactions with the ribosome. Here, we combine biophysical methods with cryo-EM structure determination to show that folding of a β-barrel protein begins with formation of a dynamic α-helix inside the ribosome. As the growing peptide reaches the end of the tunnel, the N-terminal part of the nascent chain refolds to a β-hairpin structure that remains dynamic until its release from the ribosome. Contacts with the ribosome and structure of the peptidyl transferase center depend on nascent chain conformation. These results indicate that proteins may start out as α-helices inside the tunnel and switch into their native folds only as they emerge from the ribosome. Moreover, the correlation of nascent chain conformations with reorientation of key residues of the ribosomal peptidyl-transferase center suggest that protein folding could modulate ribosome activity.


Agirrezabala, X., Samatova, E., Macher, M., Liutkute, M., Maiti, M., Gil-Carton, D., Novacek, J., Valle. M., and Rodnina, M.V.: EMBO J. (2022) e109175,

More publications Research Highlights archive

Reader’s Corner

literature to read, science to follow

In this section, a distinct selection of six highly stimulating research publications and reviews published during past 6 months is presented. It is our hope that links to exciting science, which deserves attention of the structural biology community, will help you to locate gems in the steadily expanding jungle of scientific literature. You are welcome to point out to any paper you found interesting by sending a link or citation to The section is being updated regularly.


6 Apr

Imaging active site chemistry and protonation states: NMR crystallography of the tryptophan synthase alpha-aminoacrylate intermediate (PNAS)

NMR-assisted crystallography—the integrated application of solid-state NMR, X-ray crystallography, and first-principles computational chemistry—holds significant promise for mechanistic enzymology: by providing atomic-resolution characterization of stable intermediates in enzyme active sites, including hydrogen atom locations and tautomeric equilibria, NMR crystallography offers insight into both structure and chemical dynamics. Here, this integrated approach is used to characterize the tryptophan synthase α-aminoacrylate intermediate, a defining species for pyridoxal-5′-phosphate–dependent enzymes that catalyze β-elimination and replacement reactions. For this intermediate, NMR-assisted crystallography is able to identify the protonation states of the ionizable sites on the cofactor, substrate, and catalytic side chains as well as the location and orientation of crystallographic waters within the active site. Most notable is the water molecule immediately adjacent to the substrate β-carbon, which serves as a hydrogen bond donor to the ε-amino group of the acid–base catalytic residue βLys87. From this analysis, a detailed three-dimensional picture of structure and reactivity emerges, highlighting the fate of the L-serine hydroxyl leaving group and the reaction pathway back to the preceding transition state. Reaction of the α-aminoacrylate intermediate with benzimidazole, an isostere of the natural substrate indole, shows benzimidazole bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. When modeled into the benzimidazole position, indole is positioned with C3 in contact with the α-aminoacrylate Cβ and aligned for nucleophilic attack. Here, the chemically detailed, three-dimensional structure from NMR-assisted crystallography is key to understanding why benzimidazole does not react, while indole does.

Reader’s Corner Archive

Quote of April

“Bad times have a scientific value. These are occasions a good learner would not miss.”

Ralph Waldo Emerson

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