Amphitrite ornata, a Marine Worm, Contains Two Dehaloperoxidase Genes

Abstract

Amphitrite ornata, a terebellid polychaete, inhabits marine environments that are contaminated by biogenically produced halometabolites. These halogenated organic compounds are toxic and quite diverse. To survive in this environment, A. ornata produces a novel dehaloperoxidase (DHP I) that detoxifies haloaromatic compounds. In this study we identified and characterized two dehaloperoxidase genes, designated dhpA and dhpB, from an A. ornata complementary DNA library. The deduced amino acid sequences (DHP A and DHP B) of the two dhp genes both contain 137 amino acid residues, but they differ at 5 amino acid positions. Allelic variation was observed for both genes as well. Polymerase chain reaction-restriction fragment length polymorphism assays of genomic DNA from 19 in individuals showed that each individual contains both the dhpA and the dhpB genes. Therefore, the two types of DHP are encoded by separate genes and are not alleles of a single gene. Furthermore, DHP A and DHP B may have different substrate specificities since they have amino acid differences in the active site.

Structure of dehaloperoxidase B at 1.58 Å resolution and structural characterization of the AB dimer fromAmphitrite ornata

“…In addition to being the coelomic hemoglobin of this marine worm (Weber et al, 1977), DHP possesses a biologically relevant peroxidase activity in that it catalyzes the oxidative degradation of trihalophenols to dihaloquinones . Whereas A. ornata has been shown to possess two genes, dhpA and dhpB (Han et al, 2001), that encode dehaloperoxidase isoenzymes A and B, respectively, only isoenzyme A has been characterized structurally. Thus, in order to support recent and ongoing detailed mechanistic investigations (Feducia et al, 2009;D'Antonio et al, 2010;Osborne et al, 2009) and to provide further insight into the molecular details of the protein environment that support a bifunctional heme active site, we present here the structural characterization of DHP B both as a homodimer and as a heterodimer crystallized with isoenzyme A.…”

“…However, two isoforms of dehaloperoxidase, termed DHP A and DHP B, occur in A. ornata and are encoded by two separate genes (dhpA and dhpB; Han et al, 2001). Both have been shown to catalyze the oxidative dehalogenation of 2,4,6-trihalogenated phenols to the corresponding 2,6-dihalo-1,4-benzoquinones in the presence of hydrogen peroxide (Feducia et al, 2009;D'Antonio et al, 2010).…”

Tyrosyl Radicals in Dehaloperoxidase

“…1), only three (Tyr-28, Tyr-34, and Tyr-38) are reasonably close (Ͻ10 Å) to the heme to reduce Compound I (the remaining two, Tyr-16 and Tyr-107, are at distances Ͼ15 Å away from the heme). As the DHP B isoenzyme bears an Asn at position 34 (42), only Tyr-28 and Tyr-38 were hypothesized as the likely site(s) for free radical formation (37). Thus, the experimental strategy employed herein focuses on altering radical formation in DHP via site-directed mutagenesis of three tyrosine residues, Tyr-28, Tyr-34, and Tyr-38, singly or in combinations, in both isoforms.…”

Thin-layer spectroelectrochemistry of the Fe(III)/Fe(II) redox reaction of dehaloperoxidase-hemoglobin

“…In light of the mandatory role played by Fe(IV)-based catalysis in globin-based biosensors (vide supra), DHP may represent an attractive target protein for the development of more efficient devices of this kind. In A. ornata, two genes (dhp A and dhp B) [40] code for slightly different DHP isoforms (DHP A and DHP B), both of which exhibit enhanced peroxidase activity [41]. All data reported herein pertain to the DHP A isoform.…”