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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Researchers built an artificial metalloenzyme by adding a copper-binding unnatural amino acid to the LmrR protein scaffold. In laboratory tests, the resulting catalyst promoted an enantioselective, vinylogous Friedel–Crafts alkylation of indole derivatives—but its performance depended strongly on which indole was used. The work was a proof of concept, not evidence of an industrial process or a commercially available technology.
How the artificial metalloenzyme was built
The study by Ivana Drienovská, Ana Rioz-Martínez, Apparao Draksharapu and Gerard Roelfes used genetic-code expansion to incorporate a non-proteinogenic, metal-binding amino acid into LmrR, a protein scaffold. Amber stop-codon suppression enabled the engineered protein to be produced with that unnatural amino acid in a chosen position. The researchers then combined the protein with copper to create an artificial metalloenzyme: a constructed catalyst, not a naturally evolved enzyme.
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The design brings together two kinds of catalytic influence. Copper provides metal-based reaction chemistry, while the protein creates a chiral, hydrophobic environment around the catalytic site. That surrounding environment can influence which of two mirror-image product forms is favored. The original report appeared as a Chemical Science Edge Article in 2015, DOI 10.1039/C4SC01525H. A Royal Society of Chemistry blog post about the work was published on 18 November 2014: RSC Chemical Science blog.
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What reaction it catalysed
The team examined a vinylogous Friedel–Crafts alkylation involving indole derivatives. Friedel–Crafts reactions form carbon–carbon bonds by adding an aromatic compound to an electrophile; in a vinylogous version, reaction occurs through a conjugated system at a position farther from the initial site of activation. The study’s asymmetric catalyst also favored one enantiomer—the molecule’s mirror-image form—over the other in some substrate combinations.
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Gerard Roelfes, identified by the RSC as the University of Groningen researcher who led the study, described the motivation this way: “Nature is extremely good at catalysing reactions with very high rate accelerations and very high selectivity. But it does so, from our perspective, with a relatively limited set of reactions.” Artificial metalloenzymes offer a way to explore reactions that natural enzymes do not commonly perform while using a protein environment to shape selectivity.
Results varied sharply by indole substrate
The reported figures show why the catalyst should not be described as broadly effective across indoles. For 2-methylindole, two LmrR variants delivered high conversion and enantiomeric excess (ee), a measure of how strongly one enantiomer predominates. By contrast, the tested 5-chloroindole gave very low conversion. The paper’s table reports averages of two independent experiments, each performed in duplicate.
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| Indole substrate | LmrR variant | Conversion | Enantiomeric excess (ee) |
|---|---|---|---|
| 2-methylindole | LmrR_LM_M89X_Cu(II) | 92 ± 4% | 80 ± 2% |
| 2-methylindole | LmrR_LM_M89X_F93W_Cu(II) | 94 ± 8% | 83 ± 0% |
| 5-chloroindole | Three listed variants | 2–5% | 21–50% |
| Another tested indole | Listed variants | 11–16% | 49–55% |
These are experimental results for the tested substrate and catalyst combinations, not general performance guarantees. The researchers described 2-methylindole as especially compatible with the protein pocket and 5-chloroindole as a poor substrate. They also noted that such substrate specificity is a drawback when broad reaction scope is the goal.
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Laboratory conditions and what they imply
Typical reported conditions used 9 mol% Cu(H₂O)₆(NO₃)₂ at 90 μM, 1.25 equivalents of an LmrR variant measured in monomer, 20 mM MOPS buffer at pH 7.0 and 150 mM NaCl. Reactions ran for three days at 4 °C. These cold, buffered laboratory conditions establish that the designed system could catalyse the reaction under the study’s experimental setup; they do not establish a scaled manufacturing method, economic viability or performance under industrial conditions.
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How the work fits into later research
Subsequent studies explored related questions, but their findings should not be attributed to the 2015 LmrR experiment. A 2020 report examined Cu(II) with the TetR-family proteins CgmR, RamR and QacR, without an external ligand. It reported enantioselective vinylogous Friedel–Crafts alkylation with up to 75% ee and proposed that electrostatic and π-stacking interactions in the protein’s second coordination sphere help bind the copper–substrate complex. See the 2020 TetR-family study.
Another 2020 study of LmrR investigated how the position of an abiological metal cofactor affected reaction preference. It considered indole Friedel–Crafts alkylation with β-substituted enones as well as tandem alkylation and enantioselective protonation with α-substituted enones. The researchers reported that a single protein mutation could specialize the artificial metalloenzyme toward one of those reaction types. This later work points to continued catalyst-design research, not commercial availability. See the 2020 LmrR cofactor-position study.
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What the result does—and does not—show
The 2015 study demonstrates a strategy for combining an unnatural metal-binding amino acid, copper and a protein scaffold to catalyse an asymmetric reaction outside the usual repertoire of natural enzymes. Its strongest reported results applied to a particular indole substrate, while other tested substrates performed much worse. The cited studies establish laboratory research; they do not establish a marketed enzyme, consumer kit or industrial deployment.
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