4FH7: Structure Of Dhp A In Complex With 2,4,6-tribromophenol In 20% Methanol

Citation:
Abstract
X-ray crystal structures of dehaloperoxidase-hemoglobin A (DHP A) from Amphitrite ornata soaked with substrate, 2,4,6-tribromophenol (2,4,6-TBP), in buffer solvent with added methanol (MeOH), 2-propanol (2-PrOH), and dimethyl sulfoxide (DMSO) reveal an internal substrate binding site deep in the distal pocket above the alpha-edge of the heme that is distinct from the previously determined internal inhibitor binding site. The peroxidase function of DHP A has most often been studied using 2,4,6-trichlorophenol (2,4,6-TCP) as a substrate analogue because of the low solubility of 2,4,6-TBP in an aqueous buffer solution. Previous studies at low substrate concentrations pointed to the binding of substrate 2,4,6-TCP at an external site near the exterior heme beta- or delta-edge as observed in the class of heme peroxidases. Here we report that the turnover frequencies of both substrates 2,4,6-TCP and 2,4,6-TBP deviate from Michaelis-Menten kinetics at high concentrations. The turnover frequency reaches a maximum in the range of 1400-1700 muM, with a decrease in rate at higher concentrations that is both substrate- and solvent-dependent. The X-ray crystal structure is consistent with the presence of an internal active site above the heme alpha-edge, in which the substrate would be oxidized in two consecutive steps inside the enzyme, followed by attack by H2O via a water channel in the protein. The physiological role of the internal site may involve interactions with any of a number of aromatic toxins found in benthic ecosystems where A. ornata resides.
PDB ID: 4FH7Download
MMDB ID: 108647
PDB Deposition Date: 2012/6/5
Updated in MMDB: 2013/04
Experimental Method:
x-ray diffraction
Resolution: 1.74  Å
Source Organism:
Similar Structures:
Biological Unit for 4FH7: dimeric; determined by author
Molecular Components in 4FH7
Label Count Molecule
Proteins (2 molecules)
2
Dehaloperoxidase a
Molecule annotation
Chemicals (16 molecules)
1
2
2
1
3
1
4
8
5
4
* Click molecule labels to explore molecular sequence information.

Citing MMDB
.