Light-Activated Proteomic Labeling via Photocaged Bioorthogonal Non-Canonical Amino Acids.

This work introduces light-activated bioorthogonal noncanonical amino acid tagging (laBONCAT) as a method to selectively label, isolate, and identify proteins newly synthesized at user-defined regions in tissue culture. By photocaging l-azidohomoalanine (Aha), metabolic incorporation into proteins is prevented. The caged compound remains stable for many hours in culture, but can be photochemically liberated rapidly and on demand with spatial control. Upon directed light exposure, the uncaged amino acid is available for local translation, enabling downstream proteomic interrogation via bioorthogonal conjugation. Exploiting the reactive azide moiety present on Aha's amino acid side chain, we demonstrate that newly synthesized proteins can be purified for quantitative proteomics or visualized in synthetic tissues with a new level of spatiotemporal control. Shedding light on when and where proteins are translated within living samples, we anticipate that laBONCAT will aid in understanding the progression of complex protein-related disorders.

Photomediated oxime ligation as a bioorthogonal tool for spatiotemporally-controlled hydrogel formation and modification.

Click chemistry has proved a valuable tool in biocompatible hydrogel formation for 3D cell culture, owing to its bioorthogonal nature and high efficiency under physiological conditions. While traditional click reactions can be readily employed to create uniform functional materials about living cells, their spontaneity prohibits spatiotemporal control of material properties, thereby limiting their utility in recapitulating the dynamic heterogeneity characteristic of the in vivo microenvironment. Photopolymerization-based techniques gain this desired level of 4D programmability, but often at the expense of introducing propagating free radicals that are prone to non-specific reactions with biological systems. Here we present a strategy for bioorthogonal hydrogel formation and modification that does not rely on propagating free radicals, proceeding through oxime ligation moderated by a photocaged alkoxyamine. Upon mild near UV light exposure, the photocage is cleaved, liberating the alkoxyamine and permitting localized condensation with an aldehyde. Multi-arm crosslinkers, functionalized with either benzaldehydes or photocaged alkoxyamines, formed oxime-based hydrogels within minutes of light exposure in the presence of live cells. Polymerization rates and final mechanical properties of these gels could be systematically tuned by varying crosslinker concentrations, light intensity, aniline catalyst equivalents, and pH. Moreover, hydrogel geometry and final mechanical properties were controlled by the location and extent of UV exposure, respectively. Photomediated oxime ligation was then translated to the biochemical modification of hydrogels, where full-length proteins containing photocaged alkoxyamines were immobilized in user-defined regions exposed to UV light. The programmability afforded by photomediated oxime ligation can recapitulate dynamically anisotropic mechanical and biochemical aspects of the native extracellular matrix. Consequently, photopolymerized oxime-based hydrogels are expected to enable an enhanced understanding of cell-matrix interactions by serving as improved 4D cell culture platforms.