Specific labeling of proteins within living cells with single residue precision through genetically encoded click chemistry

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The development of catalyst-free click chemistry, i.e. a chemical reaction that is non-toxic and proceeds readily and specifically even within living organisms, has revolutionized chemical biology. By encoding strained alkyne unnatural amino acids (UAAs) into the genetic repertoire of the cell, we exploited this chemistry to label proteins with single residue specificity in bacteria and mammalian cells. In the past years we extended the method to more click type reactions, namely of the Diels-Alder type, improved some of the technical shortcomings, and applied the novel UAAs to time-dependent growth factor receptor labeling on the surface of intact mammalian cells. In this proposal extension, we aim to further improve the cellular protein labeling technique by synthesizing new UAAs as well as fluorescent labeling reagents with a reduced tendency to interact with cell compartments and protein epitopes unspecifically. We will continue to improve the tRNA synthetases necessary for introducing UAAs to proteins and we will provide stable cell lines expressing tRNA and tRNA synthetases. The combined improvements will help to provide site-specific click-mediated fluorescent labeling to a broad range of applications, including superresolution microscopy.