The noncanonical amino acid S-allyl cysteine (Sac) is one of the major compounds of garlic extract and exhibits ar ange of biological activities. It is also as mall bioorthogonal alkene tag capable of undergoing controlled chemical modifications, such as photoinduced thiol-ene coupling or Pd-mediated deprotection. Its small size guarantees minimal interference with protein structure and function. Here, we report as imple protocol efficiently to couple in-situ semisynthetic biosynthesis of Sac and its incorporation into proteins in response to amber (UAG) stop codons. We exploitedt he exceptional malleability of pyrrolysyl-tRNA synthetase (PylRS) and evolved an S-allylcysteinyltRNA synthetase (SacRS) capable of specifically acceptingt he small, polar amino acid instead of its long andb ulky aliphatic natural substrate. We succeeded in generating an ovel and inexpensive strategy for the incorporation of af unctionally versatile amino acid. This will help in the conversiono fo rthogonal translation from as tandard technique in academic research to industrial biotechnology.
The precision of single-molecule localization-based super-resolution microscopy, including dSTORM, critically depends on the number of detected photons per localization. Recently, reductive caging of fluorescent dyes followed by UV-induced recovery in oxidative buffer systems was used to increase the photon yield and thereby the localization precision in single-color dSTORM. By screening 39 dyes for their fluorescence caging and recovery kinetics, we identify novel dyes that are suitable for multicolor caged dSTORM. Using a dye pair suited for registration error-free multicolor dSTORM based on spectral demixing (SD), a multicolor localization precision below 15 nm was achieved. Caged SD-dSTORM can resolve the ultrastructure of single 40 nm synaptic vesicles in brain sections similar to images obtained by immuno-electron microscopy, yet with much improved label density in two independent channels.
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