Vanadium bromoperoxidase active site

Figure 17.13 The structure and active site of the bromoperoxidase subunit from C. pilulifera. Residues conserved in all vanadium bromo- and chloroperoxidases are in grey, those that vary in cyan. (From Ohshiro et al., 2004. Copyright 2004 The Protein Society.)...

The haloperoxidases are a class of enzymes that catalyze the oxidation of halides via a reactive peroxometal active site. These enzymes are named according to the most electronegative halide they are able to oxidize. Hence, a bromoperoxidase can oxidize bromide and iodide but not chloride, whereas a chloroperoxidase can oxidize all three. Haloperoxidases are found in most living organisms and predominately fall into two classes the iron heme-based and vanadium-dependent enzymes. Of these, heme-based enzymes are found in mammals, where they provide a vital... 

Figure 1. Proposed structure of the active site of vanadium bromoperoxidase based on EXAFS data (17).

The X-ray structures of vanadium bromoperoxidases from the red seaweeds Corallina pilulifera and C. officinalis have also been determined and their structures are almost identical. The native structure of these enzymes is dodecameric and the structure is made up of 6 homo-dimers. The secondary stmcture of the chloroperoxidase from the ftmgus Curvularia inaequalis that will be discussed later can be superimposed with the Corallina hromoperoxidase dimer. Many of the a helices of each chloroperoxidase domain are structurally equivalent to the a helices in the Corallina hromoperoxidase dimer. This is in line with the evolutionary relationship between the haloperoxidases that will be discussed later. The disulfide bridges in the enzyme from A. nodosum are not found in the enzyme from Corallina and the two remaining cysteine residues are not involved in disulfide bonds. Additionally, in this enzyme binding sites are present for divalent cations that seem to be necessary to maintain the stmcture of the active site cleft. All the residues directly involved in the binding of vanadate are conserved in the algal bromoperoxidases. ... 

The X-ray structme analysis of the active site (Figme 7a) shows that vanadium is bound as orthovanadate in the same way as in the bromoperoxidases in which three oxygen atoms form a plane (bond length about 1.65 A), the fourth oxygen is found at the apex (bond length 1.93 A) which is in the range... 

Fig. 2. Proposed structure for the active site in vanadium bromoperoxidase according to Ref. 48 and slightly modified.

The EXAFS data showed the presence of multiple scattering effects from outer atoms of a group corresponding to a histidine ligated to vanadium. Also the ESEEM experiments clearly indicated the presence of a histidine residue in the active site as confirmed now by the X-ray structure of the vanadium bromoperoxidase from Ascophyllum nodosum ... 

Figure 3 The active site residues around the vanadate center of vanadium bromoperoxidase from A. nodosum. There are aiso three water molecules (W772, VsIllS and W761) in the active site. (Reprinted from Ref. 24, 1999, with permission from Elsevier)...

Recent papers describe models for molybdenum-containing enzymes [106], Certain vanadium complexes have been described to mimic the binding site reactions of vanadium haloperoxidases [62, 107], Scheme XI.20 demonstrates the mechanism of active species formation in bromoperoxidase proposed on the basis of the investigation of model reactions [108],... 

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