Artificial metalloenzymes, made from protein scaffolds incorporating synthetic metal complexes, combine the versatility of transition-metal catalysts with the shape selectivity of enzymes. Until now, getting the metal complex into the cell has been difficult, and the reactivity of artificial enzymes in living cells has been limited. John Hartwig and colleagues use living cells of EcN, a non-pathogenic strain of E. coli, as reaction vessels to assemble artificial metalloenzymes that catalyze further chemical reactions (DOI: 10.1021/jacs.1c10975).
An iridium-containing porphyrin enters the bacterial cells from the growth medium via a chromosomally encoded outer-membrane transporter. The resulting enzyme catalyst drives site-selective, enantioselective carbene insertion into benzylic C–H bonds. The authors also identify a new transporter that is more efficient at taking iridium porphyrins into the cell cytoplasm than the heme transporter that they had originally assumed was the conduit.
Using EcN as a whole-cell screening platform eliminates the need for laborious processing procedures. This drastically increases the ease and throughput of screening artificial metalloenzymes to identify species with the best catalytic properties. This research presents a way to use biological systems to assemble similar catalysts, and it broadens the applications of artificial metalloproteins in catalyst-assisted organic reactions.