Bromoperoxidase structure

Figure 4 Stabilized bromine antimicrobials are produced by eosinophils, a type of mammalian white blood cell. Bacteria are captured by phagocytosis and contained intracellularly within vesicles called phagosomes. Granules release cationic surfactants, lytic enzymes, and eosinophil peroxidase into the phagosome in a process known as degranulation. Eosinophil peroxidase, an enzyme that is structurally similar to the bromoperoxidases found in seaweed (Figure I), selectively catalyzes oxidation of bromide to hypobromite by reducing hydrogen peroxide to water. The hypobromite immediately reacts with nitrogenous stabilizers such as aminoethanesulfonic acid (taurine) to form more effective and less toxic antimicrobial agents.

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.)...

Butler, A. Baldwin, A.H. (1997)Vanadium Bromoperoxidase and Functional Mimics. In Structure and Bmiding Metal Sites in Proteins and Models, Lewis Acids, and Vanadium, Sadler, P., Hill, H.A.O., Thompson, A., eds. Springs-Vwlag, New York, Volume 89, pp. 109-131. 

Isupov MN, Dalby AR, Brindley AA, Izumi Y, Tanabe T, Murshudov GN, Littlechild JA (2000) Crystal Structure of Dodecameric Vanadium-dependent Bromoperoxidase from the Red Algae Corallina officinalis. J Mol Biol 299 1035... 

Kimblin C, Bu X, Butler A (2002) Modeling the Catalytic Site of Vanadium Bromoperoxidase Synthesis and Structural Characterization of Intramolecularly H-bonded Vanadium (V) Oxoperoxo Complexes, [V0(02)(NH2pyg2)]K and [V0(02)(BrNH2pyg2)]K. Inorg Chem 41 161... 

Two vanadium bromoperoxidases that differ in carbohydrate content [26,33] have been isolated from A. nodosum. The most abundant bromoperoxidase, V-BrPO-I, was found in the thallus, and the other bromoperoxidase, V-BrPO-II, was reported to be present on the thallus surface [26], A previous report also concluded that V-BrPO is present in two different locations of A. nodosum, one in the cell walls of the transitional region between the cortex and medulla of the thallus and the other in the cell wall of the thallus surface [34], More recent experiments demonstrate that vanadium-dependent bromoperoxidase activity is present in both the cortical and surface protoplasts of M. pyrifera [35], L. saccharina, and L. digitata [36], The biosynthesis of V-BrPO in the protoplasts of L. saccharina has been shown using [35S]-methionine [36], The vanadium bromoperoxidases are all acidic proteins [26] with very similar amino acid compositions [37], V-BrPO (A. nodosum) has been crystallized, although refined structural data have not been reported yet [38], A different isolation procedure, based primarily on a two-phase extraction system, has been described [39,40], This procedure works well for certain types of algae (e.g., Laminaria) but not for the isolation of V-BrPO from A. nodosum, the principal source of V-BrPO for the mechanistic studies. 

Kimblin, C., X. Bu, and A. Butler. 2002. Modeling the catalytic site of vanadium bromoperoxidase Synthesis and structural characterization of intramolecularly H-bonded vanadium(V) oxoperoxo complexes, [VO(()2)(NI I2pyg2) K and [VO(02) (BrNH2pyg2)]K. Inorg. Chem. 41 161-163. 

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

Some Structural Considerations Concerning Model Compounds and Vanadium Bromoperoxidase... 

The extant literature of vanadium coordination complexes can be used to shed additional light on the vanadium site of vanadium bromoperoxidase. The known structures of vanadium in a variety of coordination environments provide a wealth of structural detail that can be brought to bear on the proposed enzyme structure. 

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. ... 

Attempts to model the structure of the V-dependent bromoperoxidase enzyme have resnlted in the characterization by X-ray crystallography of a great number of VO + complexes having N,N,N,N-donor atoms. The imidazole group is thought to mimic the protein enviromnent and complexes such as [VO(SALIMH)(acac)(MeOH)], [VO(SALIMH)SAL], and [VO(SALIMH)2(EtOH)], have been prepared " (see Vanadium in Biology). 

Figure 7 Powder spectrum of V-bromoperoxidase. Spectrum is axial (g < gi) with hyperfine structure (8 lines from / = 7/2) on...

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

It is obvious that the proposed structure of the active site in the enzyme can only be confirmed when the three-dimensional structure of bromoperoxidase is available. Without this, it is not possible to obtain and interpret the details of the catalytic reaction. As such the crystallization of the bromoperoxidase reported recently is a first step in this direction (93). 

Complexes of ligands with O-donors and two or three N-donors are known. The kinetics of the outer-sphere oxidation of cis-aq uaoxovanad i u m (IV) complexes of [2-(pyridylmethyl)imino]diacet-ate and its derivatives were determined.675 Complexes with Schiff bases have been used to mimic the structure and chemistry of vanadium bromoperoxidase.275 The ligation of an imidazole functionality in the ligand has been found to readily dissociate, and is important to the functional aspects of this complex.275 A variety of five-coordinate complexes with tridentate Schiff base complexes have been prepared, several of which have been found to form supramolecular polymeric structures through association between the V=0 groups in a V=0 V=0 V=0 pattern (140).627... 

The active sites of the bromoperoxidase from A. nodosum (a), the chloroperoxidase from Cur. inaequalis (b) and its peroxo form (c). In (c), amino acids proposed to play a role in the activation of peroxide are indicated. Tryptophan (Trp350/Trp338) is replaced by arginine (Arg395) in the bromoperoxidase from the red alga Cor. officinalis. The structure in (d) is based on XAS and EPR data for the reduced, inactive form of the A. nodosum enzyme. See Table 4.5 for structure parameters and references. 

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 ... 

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