Hole hopping along chains of tryptophan (Trp) and tyrosine (Tyr) residues is a critical function in several metalloenzymes that generate high-potential intermediates by reactions with O2 or H2O2. In many cases these chains may serve a protective role in metalloenzymes by deactivating high-potential reactive intermediates formed in uncoupled catalytic total turnovers. The Trp/Tyr network connectivity map for bacterial cytochrome P450BM3 indicates that this enzyme has a closely spaced Trp/Tyr triad (W96, W90 and Y334) from the heme to the protein surface. This Trp/Tyr triad can potentially form a functional radical transfer pathway, which protects the enzyme from damage under circumstances in which high-potential heme intermediates are produced, but substrate is not oxidized. Comparing wild-type P450BM3 with three mutants (W96H, W90F and Y334F), we showed that total turnover numbers decrease in the mutants. We suggest that W96, W90 and Y334 could be involved as redox intermediates in multistep electron transfer events, thereby steering high-potential oxidizing equivalents away from the enzyme active site.

Protective hole hopping in full-length cytochrome P450BM3

ACS Spring 2022

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