Our group has spent years developing precise and backgroundless bioconjugation chemistry, but metalloenzymes present a special challenge: labeling cysteine without disrupting the metal-bound cysteines that support the active site.  In our new paper that just appeared in @Chem_CP, Nima Adhami and colleagues show that organometallic Au(III) aryl complexes selectively label cysteine while leaving metal-bound cysteines in the metalloenzyme active sites untouched: cell.com/chem/fulltext/S2451…. A favorite highlight from this work: a single-crystal X-ray structure of a labeled metalloenzyme with an abiotic crown ether positioned on a Cys residue. This is the first X-ray structure of a protein modified by organometallic cysteine arylation!  Shout-out goes to all amazing collaborators on this work including: @JoeLoo85614818, @Jose54509762, @ShafaatLab and their teams.