| Title: |
The {FeO2}8 Intermediate of the TxtE Nitration Pathway Resists Reduction, Facilitating Its Reaction with Nitric Oxide |
| Authors: |
Yousong Ding (10034709); Jonathan Caranto (10018673); Rosemary Loria (10040914); Manyun Chen (10040917); Christopher Martin (10040918); Maria Martinez (10040920) |
| Publication Year: |
2021 |
| Collection: |
Smithsonian Institution: Digital Repository |
| Subject Terms: |
Bioinorganic Chemistry; Nitric oxide; Metalloenzymology; natural product; nitration mixture; Streptomyces |
| Description: |
TxtE is a cytochome P450 (CYP) homolog that mediates a nitric oxide (NO)-dependent direct nitration of l-tryptophan (l-Trp) to form 4-nitrotryptophan (4-NO 2 -l-Trp). This nitrated product is a precursor for thaxtomin A, a virulence factor produced by plant-pathogenic bacteria that causes the disease potato scab. A recent study provided the first characterization of intermediates along the TxtE nitration pathway. 1 The authors’ accumulated evidence supported a mechanism in which O 2 binds to Fe II TxtE to form an {FeO 2 } 8 intermediate, which subsequently reacted with NO to ultimately form Fe III TxtE and 4-NO 2 -l-Trp. Typical CYP mechanisms reduce and protonate the {FeO 2 } 8 intermediate to form a ferric-hydroperoxo species (Fe III –OOH) en route to formation of the active oxidant compound I. The previously reported lack of hydroxylated tryptophan resulting from TxtE turnover suggests that the TxtE cycle must stall at the {FeO 2 } 8 intermediate to avoid hydroxylation. Here we present LC-MS experiments showing suggesting that TxtE can hydroxylate l-Trp by the peroxide shunt but not via reduction of the {FeO 2 } 8 intermediate. Comparison of stopped-flow time courses in the presence and absence of excess reducing equivalents and common CYP electron transfer partners shown no spectral or kinetic evidence for reduction of the {FeO 2 } 8 intermediate. Furthermore, the electron coupling efficiency of TB14—a self-sufficient TxtE variant with C-terminal reductase domain—to form 4-NO 2 -l-Trp exhibits a 3% electron coupling efficiency when it is loaded with one reducing equivalent. This efficiency increases by 2-fold when TB14 is loaded with two or four reducing equivalents. This observation provides further evidence for our key conclusion that the TxtE {FeO 2 } 8 intermediate resists reduction. The resistance of the {FeO 2 } 8 intermediate to reduction is a key feature of TxtE, enabling reaction with NO and efficient nitration turnover. |
| Document Type: |
report |
| Language: |
unknown |
| Relation: |
https://figshare.com/articles/preprint/The_FeO2_8_Intermediate_of_the_TxtE_Nitration_Pathway_Resists_Reduction_Facilitating_Its_Reaction_with_Nitric_Oxide/13637867 |
| DOI: |
10.26434/chemrxiv.13637867.v1 |
| Availability: |
https://doi.org/10.26434/chemrxiv.13637867.v1 |
| Rights: |
CC BY-NC-ND 4.0 |
| Accession Number: |
edsbas.57FB5A32 |
| Database: |
BASE |