Project Summary/AbstractBiocompatible chemical transformations that are promoted by light have become powerful tools in chemicalbiology by virtue of enabling spatiotemporal control over activity. Whilst genetically encoded photoactivatabletools have become mainstays in the bio-orthogonal toolbox light driven conjugation methods that effectivelyinterface with native biomolecular structures (no genetic encoding) under biologically relevant conditions arecomparatively limited. In this project we will evolve a method recently developed by our group for thephotobioconjugation of Tryptophan (Trp) residues using redox-active N-carbamoylpyridinium salts that engageTrp in photo-induced electron transfer. We will show that by carefully modulating the optical and electrochemicalproperties of these reagents that we will be able to both (1) dramatically enhance the kinetic capabilities of thislabelling reaction and (2) enable the discovery of new mechanistic paradigms that promote this labellingchemistry. Moreover we will demonstrate that through careful manipulation of optical and electrochemicalproperties of the N-carbamoyl pyridinum salt reagent that we will be able to invoke mechanistic control over Trplabelling in a wavelength-dependent fashion (i.e. we can control reaction mechanism with a given wavelengthof light). This in turn will allow us to design new application-based experiments that can both command precisereaction outcomes and markedly expand the capabilities of photobioconjugation chemistry. Specifically we willharness this optical and mechanistic control for the design of new activity-based sensing applications as well asthrough the design of proximity labelling approaches that we apply to the study of poorly understood processesin mitochondrial dynamics.