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CHEMICAL BIOLOGY SYNTHETIC BIOLOGY Proximity labeling with Engineering wild bacteria TurboID Brophy, J. A. N. et al. Nat. Microbiol. 3, Branon, T. C. et al. Nat. Biotechnol. 36, 1043–1053 (2018). 880–887 (2018). Undomesticated bacteria have a very wide Enzyme-catalyzed proximity labeling range of properties that could be exploited has rapidly become a popular approach for research, medicine, and technology with for studying the spatial localization and some engineering, but most of the bacteria interactions of in the cell. In this in the wild are difficult if not impossible technique, a of interest is labeled with to genetically manipulate. To address this, a promiscuous enzyme that adds a tag such Brophy et al. take advantage of conjugation, as to near-neighbor proteins, thereby the natural process of DNA transfer between enabling their purification and identification bacteria that secretes a protein–DNA by mass spectrometry. Although several complex from a donor to a recipient cell. systems are now available, the most They designed a Bacillus subtilis strain, commonly used approaches are APEX, XPORT, with a mobile integrative and which uses an ascorbate peroxidase and conjugative element (ICE) and used it to offers rapid tagging kinetics but is limited by transfer heterologous DNA to a recipient the requirement for toxic strain, ensuring that it could not spread addition, and BioID, based on a nontoxic beyond that strain. The approach allowed biotin ligase system, which has slow tagging engineering of 52 species and 17 genera of kinetics. Branon et al. now report a system bacteria, including isolates from human gut that allows rapid nontoxic proximity labeling and skin. To illustrate a practical application, in just 10 minutes. Using , they the researchers introduce a nitrogen-fixation evolved the Escherichia coli biotin ligase pathway into various host bacteria. NR BirA to generate new promiscuous tagging https://doi.org/10.1038/s41592-018-0160-6 variants, which they dubbed TurboID and miniTurbo. The researchers demonstrate Workshops in that the TurboID system is applicable in BIOCHEMISTRY Scienti c Writing organisms including worms and flies. AD Large-sized bilayer nanodiscs https://doi.org/10.1038/s41592-018-0158-0 Zhao, Z. et al. J. Am. Chem. Soc. 140, and Publishing 10639–10643 (2018).

Delivered by Nature Research MICROSCOPY Phospholipid-bilayer nanodiscs are model membrane systems that offer a native-like journal editors and hosted Gentler super-resolution environment for the study of membrane microscopy proteins. However, the size of such synthetic at institutions worldwide, Masullo, L. A. et al. Nat. Commun. 9, 3281 (2018). bilayer nanodiscs is generally limited to less researchers learn how to than 20 nm in diameter, which hinders their Super-resolution microscopy is often application with large membrane proteins. turn great science into great considered challenging to apply to living To address this limitation, Zhao et al. used specimens because of the high, potentially a DNA origami scaffold to assist in the papers. toxic light doses and long collection times formation of stable nanodiscs with a diameter typically used to generate images. Masullo of ~70 nm. They used a DNA origami barrel et al. addressed this challenge by developing as a scaffolding corral to recruit a number the ‘molecular nanoscale live imaging with Find out more at of small (~11 nm) nanodiscs, and then used sectioning ability’ (MoNaLISA) nanoscope detergent to induce local rearrangement masterclasses.nature.com for prolonged super-resolution imaging with of the adjacent bilayers, thus allowing relatively low light intensities. MoNaLISA is neighboring nanodiscs to merge and form one conceptually similar to reversible saturable interconnected structure. The flexibility of the optical fluorescent transition (RESOLFT) DNA origami scaffold and excess lipids are microscopy, but it overcomes the limitations required for the formation of large, circular, of that approach by using light patterns with bilayer nanodiscs. The enclosed nanodiscs are optimized shapes and periodicities to control W masterclasses.nature.com relatively stable and tolerant to a broad range the reversibly switchable fluorescent proteins Follow us on LinkedIn of pH levels and divalent ion concentrations. used for labeling. The result is a microscopy The researchers applied this nanodisc system method that achieves ~50-nm resolution over to reconstitute two membrane-protein clusters entire cell volumes over long periods. The and to study poliovirus entry. LT researchers demonstrated the approach for https://doi.org/10.1038/s41592-018-0161-5 time-lapse imaging of organelles, colonies of mouse embryonic stem cells, and neurons. RS Allison Doerr, Nicole Rusk, Rita Strack, A57484 https://doi.org/10.1038/s41592-018-0159-z Lei Tang and Nina Vogt

764 Nature Methods | VOL 15 | OCTOBER 2018 | 759–765 | www.nature.com/naturemethods