Ergothioneine is an emerging factor in cellular redox homeostasis in bacteria, fungi, plants, and animals. Reports that ergothioneine biosynthesis may be important for the pathogenicity of bacteria and fungi raise the question as to how this pathway is regulated and whether the corresponding enzymes may be therapeutic targets. The first step in ergothioneine biosynthesis is catalyzed by the methyltransferase EgtD that converts histidine into N-α-trimethylhistidine. This report examines the kinetic, thermodynamic and structural basis for substrate, product, and inhibitor binding by EgtD from Mycobacterium smegmatis. This study reveals an unprecedented substrate binding mechanism and a fine-tuned affinity landscape as determinants for product specificity and product inhibition. Both properties are evolved features that optimize the function of EgtD in the context of cellular ergothioneine production. On the basis of these findings, we developed a series of simple histidine derivatives that inhibit methyltransferase activity at low micromolar concentrations. Crystal structures of inhibited complexes validate this structure- and mechanism-based design strategy.

A new single‐molecule switching concept relying on the E‐field‐dependent orientation of a push‐pull system (via its dipole moment) is presented. As first steps towards realizing the E‐field‐triggered single‐molecule motion, the synthesis of turnstile 1, which is designed to bridge a gap within a carbon nanotube junction, is reported. Turnstile 1 consists of a hexakis(m‐phenyleneethynylene) macrocycle decorated with phenanthrene‐functionalized oligo(phenyleneethynylene) (OPE) wires at opposite ends, as well as a para‐connected push‐pull rod as rotator unit. The similarity of the rotor dimension with the surrounding macrocycle guarantees efficient π‐stacking between both subunits when an E‐field is applied. To introduce a dipole moment into the rotator, the structure is terminally functionalized with a nitrile group on one side and with a dimethylamino group on the opposite end. Synthetic protocols based on Sonogashira–Hagihara couplings were developed to build up the macrocycle scaffold. The highly functionalized open precursor A is the key building block of the sequence as it allows a twofold intramolecular palladium‐catalyzed cyclization reaction to be performed to obtain the target turnstile in a very good yield of 68 %. The target structure was fully characterized by NMR spectroscopy and mass spectrometry. Furthermore, 1H‐1H NOESY NMR experiments pointed to a pseudo‐rotation of the push‐pull rod within the turnstile structure on the time scale of the NMR experiment.