Synthetic promoter based azide biosensor toolkit to advance chemical-biology

Real-time azide or azido-functionalized molecular detection inside living cells using bioorthogonal chemistry-based approaches has been revolutionary to advancing chemical-biology. These methods have enabled diverse applications ranging from understanding the role of cellular glycosylation pathways, identifying diseased cells, and targeting delivery of azido-based therapeutic drugs. However, while classical techniques were applicable only to in-vitro detection of such functional groups, even recent bioorthogonal based-detection methods require expensive sensing reagents and also cannot selectively identify inorganic azide. Here, we report an in-vivo synthetic promoter based azide biosensor toolkit to selectively detect azide anions. A promiscuous cyanate-specific promoter was engineered to detect azide and rapidly induce expression of green fluorescent protein (GFP) in Escherichia coli. Our synthetic azide operon allows highly-tunable GFP expression, outperforming the classic lac-operon, and also offers an alternative low-cost protein expression system. Finally, we showcase the utility of this toolkit for in-vivo bioorthogonal reaction biosensing and glycoengineering based applications.