A doubly responsive probe for the detection of Cys4-tagged proteins.

Recombinant proteins bearing a tag are crucial tools for assessing protein location or function. Small tags such as Cys4 tag (tetracysteine; Cys-Cys-X-X-Cys-Cys) are less likely disrupt protein function in the living cell than green fluorescent protein. Herein we report the first example of the design and synthesis of a dual fluorescence and hyperpolarized (129)Xe NMR-based sensor of Cys4-tagged proteins. This sensor becomes fluorescent when bound to such Cys4-tagged peptides, and the (129)Xe NMR spectrum exhibits a specific signal, characteristic of the biosensor-peptide association.