@article {70221, title = {A chemically switchable synthetic condensate platform for reversible protein sequestration and release}, journal = {ACS Chem Biol}, year = {2025}, month = {2025 Dec 14}, abstract = {

Creating artificial organelles that sequester and release specific proteins in response to a small molecule in mammalian cells is an attractive approach for regulating protein function. In this work, by combining phase-separated condensates formed by the tandem fusion of two oligomeric proteins with a trimethoprim (TMP)-responsive nanobody switch for GFP (LAMA; ligand-modulated antibody fragment), we developed a synthetic condensate system that initially sequesters GFP-tagged proteins within condensates and rapidly releases them into the cytoplasm upon TMP treatment. The released proteins can then be resequestered by washing out the TMP. This system enabled user-defined, temporal, rapid, and reversible control of cellular processes, including membrane ruffling mediated by exogenously expressed GFP-Vav2 and modulation of the cellular localization of endogenous ERK2-GFP generated by genome knock-in. Our results highlight the utility of the LAMA-based synthetic condensate platform as a novel, chemically switchable tool for regulating protein function through controlled protein sequestration and release in mammalian cells.

}, issn = {1554-8937}, doi = {10.1021/acschembio.5c00719}, url = {https://doi.org/10.1021/acschembio.5c00719}, author = {Fukaya, Yoko and Yoshikawa, Masaru and Aoki, Kazuhiro and Farrants, Helen and Johnsson, Kai and Tsukiji, Shinya} } @article {70083, title = {An expanded palette of bright and photostable organellar Ca2+ sensors}, journal = {eLife}, year = {2025}, month = {2025 Aug 26}, abstract = {

The use of fluorescent sensors for functional imaging has revolutionized the study of organellar Ca2+\ signaling. However, understanding the dynamic interplay between intracellular Ca2+\ sinks and sources has been hindered by the lack of bright, photostable, and multiplexed measurements in different organelles, limiting our ability to define how Ca2+\ shapes cell physiology across fields of biology. Here we introduce a new toolkit of chemigenetic organellar Ca2+\ indicators whose color is tunable by reconstituting their fluorescence with different exogenous rhodamine dye-ligands, which significantly expand the capacity for multiplexing organellar Ca2+\ measurements. These sensors, which we named ER-HaloCaMP and Mito-HaloCaMP, are optimized to report Ca2+dynamics in the endoplasmic reticulum (ER) and mitochondria of mammalian cells and neurons, and show significantly improved brightness, photostability and responsiveness when compared to current best-in-class alternatives. Using either red or far-red dye-ligands, both ER-HaloCaMP and Mito-HaloCaMP enable visualizing ER and mitochondrial Ca2+\ dynamics in neuronal axons, a subcellular location that only contains a few ER tubules and small mitochondria, structural limitations that have impaired measurements with previous red sensors. To show the expanded multiplexing capacities of our toolkit, we measured interorganellar Ca2+\ fluxes simultaneously in three different subcellular compartments in live cells, revealing that the amplitude of ER Ca2+release controls the efficacy of ER-mitochondria Ca2+\ coupling in a cooperative manner. Organellar HaloCaMPs enable also measuring Ca2+\ dynamics in intact brain tissue from flies and rodents, demonstrating their versatility across biological models. Our new toolkit provides an expanded palette of bright, photostable and responsive organellar Ca2+\ sensors, which will facilitate future studies of intracellular Ca2+\ signaling across fields of biology in health and disease.

}, doi = {10.7554/elife.107845.1}, url = {http://dx.doi.org/10.7554/eLife.107845.1}, author = {Moret, Agathe and Farrants, Helen and Fan, Ruolin and Zingg, Kelsey G and Silva, Bryon and Roselli, Camilla and Oertner, Thomas G and Gee, Christine E and Hadjieconomou, Dafni and Rangaraju, Vidhya and Schreiter, Eric R and de Juan-Sanz, Jaime} } @article {69622, title = {A modular chemigenetic calcium indicator for multiplexed in vivo functional imaging.}, journal = {Nat Methods}, year = {2024}, month = {2024 Sep 20}, abstract = {

Genetically encoded fluorescent calcium indicators allow cellular-resolution recording of physiology. However, bright, genetically targetable indicators that can be multiplexed with existing tools in vivo are needed for simultaneous imaging of multiple signals. Here we describe WHaloCaMP, a modular chemigenetic calcium indicator built from bright dye-ligands and protein sensor domains. Fluorescence change in WHaloCaMP results from reversible quenching of the bound dye via a strategically placed tryptophan. WHaloCaMP is compatible with rhodamine dye-ligands that fluoresce from green to near-infrared, including several that efficiently label the brain in animals. When bound to a near-infrared dye-ligand, WHaloCaMP shows a 7{\texttimes} increase in fluorescence intensity and a 2.1-ns increase in fluorescence lifetime upon calcium binding. We use WHaloCaMP1a to image Ca responses in vivo in flies and mice, to perform three-color multiplexed functional imaging of hundreds of neurons and astrocytes in zebrafish larvae and to quantify Ca concentration using fluorescence lifetime imaging microscopy (FLIM).

}, issn = {1548-7105}, doi = {10.1038/s41592-024-02411-6}, url = {https://doi.org/10.1038/s41592-024-02411-6}, author = {Farrants, Helen and Shuai, Yichun and Lemon, William C and Monroy Hernandez, Christian and Zhang, Deng and Yang, Shang and Patel, Ronak and Qiao, Guanda and Frei, Michelle S and Plutkis, Sarah E and Grimm, Jonathan B and Hanson, Timothy L and Tomaska, Filip and Turner, Glenn C and Stringer, Carsen and Keller, Philipp J and Beyene, Abraham G and Chen, Yao and Liang, Yajie and Lavis, Luke D and Schreiter, Eric R} } @article {67863, title = {Fluorescent chemigenetic actuators and indicators for use in living animals.}, journal = {Current Opinion in Pharmacology}, volume = {62}, year = {2022}, month = {2022 Jan 15}, pages = {159-167}, abstract = {

Fluorescent indicators and actuators provide a means to optically observe and perturb dynamic events in living animals. Although chemistry and protein engineering have contributed many useful tools to observe and perturb cells, an emerging strategy is to use chemigenetics: systems in which a small molecule dye interacts with a genetically encoded protein domain. Here we review chemigenetic strategies that have been successfully employed in living animals as photosensitizers for photoablation experiments, fluorescent cell cycle indicators, and fluorescent indicators for studying dynamic biological signals. Although these strategies at times suffer from challenges, e.g. delivery of the small molecule and assembly of the chemigenetic unit in living animals, the advantages of using small molecules with high brightness, low photobleaching, no chromophore maturation time and expanded color palette, combined with the ability to genetically target them to specific cell types, make chemigenetic fluorescent actuators and indicators an attractive strategy for use in living animals.

}, issn = {1471-4973}, doi = {10.1016/j.coph.2021.12.007}, author = {Farrants, Helen and Tebo, Alison G} } @article {67197, title = {The HaloTag as a general scaffold for far-red tunable chemigenetic indicators.}, journal = {Nature Chemical Biology}, year = {2021}, month = {2021 Apr 01}, abstract = {

Functional imaging using fluorescent indicators has revolutionized biology, but additional sensor scaffolds are needed to access properties such as bright, far-red emission. Here, we introduce a new platform for {\textquoteright}chemigenetic{\textquoteright} fluorescent indicators, utilizing the self-labeling HaloTag protein conjugated to environmentally sensitive synthetic fluorophores. We solve a crystal structure of HaloTag bound to a rhodamine dye ligand to guide engineering efforts to modulate the dye environment. We show that fusion of HaloTag with protein sensor domains that undergo conformational changes near the bound dye results in large and rapid changes in fluorescence output. This generalizable approach affords bright, far-red calcium and voltage sensors with highly tunable photophysical and chemical properties, which can reliably detect single action potentials in cultured neurons.

}, issn = {1552-4469}, doi = {10.1038/s41589-021-00775-w}, author = {Deo, Claire and Abdelfattah, Ahmed S and Bhargava, Hersh K and Berro, Adam J and Falco, Natalie and Farrants, Helen and Moeyaert, Benjamien and Chupanova, Mariam and Lavis, Luke D and Schreiter, Eric R} }