Venue: salle Pyramide – Centre Broca Nouvelle-Aquitaine
“Genetic Code Expansion and Click Chemistry for super-resolution imaging in living cells”
Optical nanoscopy has contributed significantly to our understanding of biological structures. Although steadily emerging fluorescence techniques are constantly improving spatio-temporal resolution and thus enable visualization of biological processes in real time, there are still a number of challenges to overcome .
Since the density of fluorophores controls the achievable structural resolution, efficient and specific labeling with fluorescent probes is a decisive factor in super-resolution microscopy techniques. Despite recent progress in the development of new fluorophores with superior photophysical properties, specific and efficient labeling of the molecule of interest with minimal linkage error remains a significant challenge. As the field moves towards higher spatial resolution, the effective size of the label will be the main limiting factor of super-resolution microscopy, demanding the development of efficient labeling methods with small dyes, which can be site-specifically and quantitatively attached to a protein of interest with low linkage error [2-3].
Site-specific introduction of unnatural amino acids (uAA) into proteins of interest followed by bioorthogonal click chemistry with tetrazine-dyes represents a broadly useful possibility to overcome current limitations and enable high-end fluorescence imaging with organic dyes. A particularly promising type of uAA include strained alkenes, such as trans-cyclooct-2-ene (TCO), that can react with a 1,2,4,5-tetrazine in an ultrafast, specific and bioorthogonal click reaction.
Additionally, the tetrazine moiety can elicit substantial quenching of many fluorescent dyes (e.g. red-absorbing oxazines and rhodamine derivatives) and thus be utilized for improved live-cell labeling and quantitative super-resolution imaging experiments under physiological and wash-free conditions. Furthermore, this powerful tool can be applied to improve protein-protein interaction (PPI) assays [4-5], making them faster, more accurate and easier to implement.
In conclusion, new labeling techniques will enable previously impossible experiments with unseen reactivity and specificity while preserving biological function. Advances of optical microscopy in biological science will depend crucially on advances in sample preparation and labeling.
 L Lelek, M., Gyparaki, M.T., Beliu, G. et al. Single-molecule localization microscopy. Nat Rev Methods Primers 1, 39 (2021). https://doi.org/10.1038/s43586-021-00038-x
 Beliu, G. et al. Bioorthogonal labeling with tetrazine-dyes for super-resolution microscopy. Commun Biol 2, 261 (2019). https://doi.org/10.1038/s42003-019-0518-z
 Neubert*, F., Beliu*. G., et al. Bioorthogonal click chemistry enables site-specific fluorescence labeling of functional NMDA receptors for super-resolution imaging. Angew. Chem. Int. Ed. 57, 16364–16369 (2018). https://doi.org/10.1002/anie.201808951
 Beliu G., Altrichter. S., Guixa-Gonzalez, R. et al. Tethered agonist exposure in intact adhesion/class B2 GPCRs through intrinsic structural flexibility of the GAIN domain. Mol. Cell. 81: 905–921 (2021). https://doi.org/10.1016/j.molcel.2020.12.042
 Bessa-Neto*, D., Beliu*, G. et al., Bioorthogonal labeling of transmembrane proteins with non-canonical amino acids allows access to masked epitopes in live neurons. Nature Communications (2021) https://doi.org/10.1038/s41467-021-27025-w