The α,5-dicarboxy-2-nitrobenzyl caging group, a tool for biophysical applications with improved hydrophilicity: synthesis, photochemical properties and biological characterization

Effect of Photocaged Isopropyl β-d-1-thiogalactopyranoside Solubility on the Light Responsiveness of LacI-controlled Expression Systems in Different Bacteria

Photolabile protecting groups play a significant role in controlling biological functions and cellular processes in living cells and tissues, as light offers high spatiotemporal control, is non‐invasive as well as easily tuneable. In the recent past, photo‐responsive inducer molecules such as 6‐nitropiperonyl‐caged IPTG (NP‐cIPTG) have been used as optochemical tools for Lac repressor‐controlled microbial expression systems. To further expand the applicability of the versatile optochemical on‐switch, we have investigated whether the modulation of cIPTG water solubility can improve the light responsiveness of appropriate expression systems in bacteria. To this end, we developed two new cIPTG derivatives with different hydrophobicity and demonstrated both an easy applicability for the light‐mediated control of gene expression and a simple transferability of this optochemical toolbox to the biotechnologically relevant bacteria Pseudomonas putida and Bacillus subtilis. Notably, the more water‐soluble cIPTG derivative proved to be particularly suitable for light‐mediated gene expression in these alternative expression hosts.

Peptide release upon photoconversion of 2-nitrobenzyl compounds into nitroso derivatives

The photoinduced conversion via the aci-nitro into the nitroso form was studied for 4,5-dimethoxy-2-nitrobenzyl alcohols attached to various leaving groups: amino acids histidine (NHis) and aspartate (NAsp) as well as their fluorenylmethoxycarbonyl derivatives (FHis) and (FAsp). In addition, two peptides containing either of the two amino acids were studied, carrying the photoreactive group attached to a histidine (PHis), or to an aspartate (PAsp). The aci-nitro forms with maximum at λ(aci) = 420 nm were observed for FHis and FAsp after the decay of a triplet-triplet absorption, analogous to those of other 2-nitrobenzyl type compounds. For both FHis and FAsp the quantum yield of photoconversion Φ(p) is 0.03 and for the peptides PHis and PAsp ca 0.01 and 0.005, respectively.