Organic chemistry

Enzyme

Combinatorial chemistry

Tryptophan

Active site

Halogenation

Stereochemistry

Catalysis

Computational chemistry

Protein engineering

Chemistry

Molecular dynamics

Flavin group

Amino acid

Biochemistry

Nature Catalysis

Although flavin-dependent halogenases (FDHs) are attractive for C–H bond activation, their applications are limited due to low turnover and stability. We have previously shown that leakage of a halogenating intermediate, hypohalous acid (HOX), causes FDHs to be inefficient by lessening halogenation yield. Here we employed a mechanism-guided semi-rational approach to engineer the intermediate transfer tunnel connecting two active sites of tryptophan 6-halogenase (Thal). This Thal-V82I variant generates less HOX leakage and possesses multiple catalytic improvements such as faster halogenation, broader substrate utilization, and greater thermostability and pH tolerance compared with the wildtype Thal. Stopped-flow and rapid quench kinetics analyses indicated that rate constants of halogenation and flavin oxidation are faster for Thal-V82I. Molecular dynamics simulations revealed that the V82I substitution introduces hydrophobic interactions which regulate tunnel dynamics to accommodate HOX and cause rearrangement of water networks, allowing better use of various substrates than the wildtype. Our approach demonstrates that an in-depth understanding of reaction mechanisms is valuable for improving efficiency of FDHs.                                                                  Flavin-dependent halogenases catalyse the challenging regioselective halogenation of aromatic compounds, but display low efficiency. Now, a tryptophan-halogenase with multiple catalytic improvements is obtained by engineering the intermediate transfer tunnel connecting the enzyme´s two active sites.

Mechanism-guided tunnel engineering to increase the efficiency of a flavin-dependent halogenase