Slavoff, S.A. et al. J. Am. Chem. Soc. advance online publication (18 November 2011).

Rutkowska, A. et al. Angew. Chem. advance online publication (16 November 2011).

Methods to study protein-protein interactions in their native context, that is, the living cell, are needed to understand protein function and signal transduction. Two groups recently described new tools for this application and demonstrated their use in living cells. Slavoff et al. report the use of a mutant lipoic acid ligase to catalyze the attachment of a coumarin fluorophore to a short acceptor peptide. By fusing the ligase to one protein of interest and the acceptor peptide to its putative binding partner, the researchers ensured that coumarin labeling would only occur if the two proteins specifically interact. Rutkowska et al. report a dimeric biarsenic derivative of carboxy-fluorescein, called xCrAsH, which lights up only when it is covalently bound simultaneously to two interacting proteins, each containing tetracysteine peptide motifs.