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Structure of the 2,4'-dihydroxyacetophenone dioxygenase from Alcaligenes sp. 4HAP

DOI: 10.1107/S1399004714015053 DOI Help
PMID: 25195757 PMID Help

Authors: Ronan Keegan (Research Complex at Harwell) , Andrey Lebedev (Science and Technology Facilities Council (STFC)) , Peter Erskine (Royal Free and University College Medical School, UCL, U.K) , Jingxu Guo (University College London) , S. P. Wood (bLaboratory of Protein Crystallography, UCL, U.K) , D. J. Hopper (Aberystwyth University, U.K) , S. E. J. Rigby (Uinversity of Manchester, U.K) , J. B. Cooper (Royal Free and University College Medical School, UCL, U.K)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Crystallographica Section D Biological Crystallography , VOL 70 , PAGES 2444 - 2454

State: Published (Approved)
Published: September 2014
Diamond Proposal Number(s): 8922 , 1425 , 7131

Open Access Open Access

Abstract: The enzyme 2,4'-dihydroxyacetophenone dioxygenase (DAD) catalyses the conversion of 2,4'-dihydroxyacetophenone to 4-hydroxybenzoic acid and formic acid with the incorporation of molecular oxygen. Whilst the vast majority of dioxygenases cleave within the aromatic ring of the substrate, DAD is very unusual in that it is involved in C-C bond cleavage in a substituent of the aromatic ring. There is evidence that the enzyme is a homotetramer of 20.3 kDa subunits, each containing nonhaem iron, and its sequence suggests that it belongs to the cupin family of dioxygenases. In this paper, the first X-ray structure of a DAD enzyme from the Gram-negative bacterium Alcaligenes sp. 4HAP is reported, at a resolution of 2.2 Å. The structure establishes that the enzyme adopts a cupin fold, forming dimers with a pronounced hydrophobic interface between the monomers. The catalytic iron is coordinated by three histidine residues (76, 78 and 114) within a buried active-site cavity. The iron also appears to be tightly coordinated by an additional ligand which was putatively assigned as a carbonate dianion since this fits the electron density optimally, although it might also be the product formate. The modelled carbonate is located in a position which is highly likely to be occupied by the -hydroxyketone group of the bound substrate during catalysis. Modelling of a substrate molecule in this position indicates that it will interact with many conserved amino acids in the predominantly hydrophobic active-site pocket where it undergoes peroxide radical-mediated heterolysis.

Journal Keywords: Sulfuric Acid; Hydrate; High-Pressure; Neutron Diffraction; X-Ray Diffraction

Subject Areas: Biology and Bio-materials

Instruments: I03-Macromolecular Crystallography

Other Facilities: ESRF

Added On: 25/09/2014 15:59

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