Photo-dependent protein biosynthesis using a caged aminoacyl-tRNA

Genetic Encoding of Arylazopyrazole Phenylalanine for Optical Control of Translation

An arylazopyrazole was explored for its use as an enhanced photoswitchable amino acid in genetic code expansion. This new unnatural amino acid was successfully incorporated into proteins in both bacterial and mammalian cells. While photocontrol of translation required pulsed irradiations, complete selectivity for the trans-configuration by the pyrrolysyl tRNA synthetase was observed, demonstrating expression of a gene of interest selectively controlled via light exposure.

Phototriggered release of tetrapeptide AAPV from coumarinyl and pyrenyl cages

Ala-Ala-Pro-Val (AAPV) is a bioactive tetrapeptide that inhibits human neutrophil elastase, an enzyme involved in skin chronic inflammatory diseases like psoriasis. Caged derivatives of this peptide were prepared by proper N- and C-terminal derivatisation through a carbamate or ester linkage, respectively, with two photoactive moieties, namely 7-methoxycoumarin-2-ylmethyl and pyren-2-ylmethyl groups. These groups were chosen to assess the influence of the photosensitive group and the type of linkage in the controlled photo release of the active molecule. The caged peptides were irradiated at selected wavelengths of irradiation (254, 300, and 350 nm), and the photolytic process was monitored by HPLC-UV. The results established the applicability of the tested photoactive groups for the release of AAPV, especially for the derivative bearing the carbamate-linked pyrenylmethyl group, which displayed the shortest irradiation times for the release at the various wavelengths of irradiation (ca. 4 min at 254 nm, 8 min at 300 nm and 46 min at 350 nm).

Ncm, a Photolabile Group for Preparation of Caged Molecules: Synthesis and Biological Application

Ncm, 6-nitrocoumarin-7-ylmethyl, is a photolabile protective group useful for making “caged” molecules. Ncm marries the reliable photochemistry of 2-nitrobenzyl systems with the excellent stability and spectroscopic properties of the coumarin chromophore. From simple, commercially available starting materials, preparation of Ncm and its caged derivatives is both quick and easy. Photorelease of Ncm-caged molecules occurs on the microsecond time scale, with quantum efficiencies of 0.05–0.08. We report the synthesis and physical properties of Ncm and its caged derivatives. The utility of Ncm-caged glutamate for neuronal photostimulation is demonstrated in cultured hippocampal neurons and in brain slice preparations.

Phototriggered protein syntheses by using (7-diethylaminocoumarin-4-yl)methoxycarbonyl-caged aminoacyl tRNAs

The possibility of spatiotemporally photocontrolling translation holds considerable promise for studies on the biological roles of local translation in cells and tissues. Here we report caged aminoacyl-tRNAs (aa-tRNAs) synthesized using a (7-diethylaminocoumarin-4-yl)methoxycarbonyl (DEACM)-cage compound. DEACM-caged aa-tRNA does not spontaneously deacylate for at least 4 h in neutral aqueous solution, and does not bind to the elongation factor Tu. On irradiation at ∼405 nm at 125 mW cm⁻², DEACM-aa-tRNA is converted into active aa-tRNA with a half-life of 19 s. Notably, this rapid uncaging induced by visible light does not impair the translation system. Translation is photoinduced when DEACM-aa-tRNA carrying a CCCG or a CUA anticodon is uncaged in the presence of mRNAs harbouring a CGGG four-base codon or a UAG amber codon, respectively. Protein synthesis is phototriggered in several model systems, including an in vitro translation system, an agarose gel, in liposomes and in mammalian cells.

Spatiotemporal regulation of protein synthesis would advance studies into the consequences of localised protein translation in cells and tissues. Here, Ohtsuki et al. improve on an earlier caged-tRNA design to provide caged aminoacyl-tRNAs that are rapidly uncaged by visible light.