qpo gene of Aggregatibacter actinomycetemcomitans encodes a triheme c-containing membrane-bound enzyme, quinol peroxidase (QPO) that catalyzes peroxidation reaction in the respiratory chain and uses quinol as the physiological electron donor. The QPO of A. actinomycetemcomitans is the only characterized QPO, but homologues of the qpo I-BET-762 in vivo gene are widely distributed among many gram-negative bacteria, including Haemophils ducreii, Bacteroides fragilis, and Escherichia coli. One-third of the amino acid sequence of QPO from the N-terminal end is unique, whereas two-thirds of the sequence from the C-terminal end exhibits high homology with the sequence of the diheme bacterial cytochrome c peroxidase. In order to obtain sufficient protein for biophysical studies, the present study aimed to overproduce recombinant QPO (rQPO) from A. actinomycetemcomitans in E. coli. Coexpression of qpo with E. coli cytochrome c maturation (ccm) genes resulted in the expression of an active QPO with a high yield. Using purified rQPO, we determined the midpoint reduction potentials of the three heme molecules. Aggregatibacter actinomycetemcomitans is a facultative anaerobic, CO2-requiring, gram-negative
ZD1839 cell line human pathogen that has been associated with localized aggressive periodontitis (LAP) – a severe disease that occurs in adolescents and is characterized by rapid bone and tissue destruction, ultimately resulting in the loss of teeth (Zambon, 1985). Recently, we characterized quinol peroxidase (QPO), a 53.6-kDa SPTLC1 triheme c-containing membrane-bound enzyme of A. actinomycetemcomitans that catalyzes peroxidation reactions in the respiratory chain using quinol as the physiological electron donor for the reduction of
hydrogen peroxide to water (Yamada et al., 2007). QPO is the only characterized peroxidase containing three heme molecules, and the only characterized bacterial peroxidase with a transmembrane region. It has been reported that two-thirds of the amino acid sequence at C-terminal end of QPO exhibits ∼43% sequence similarity with that of the diheme bacterial cytochrome c peroxidase (BCCP). Further, most of the key amino acid residues in BCCP are conserved in this sequence, except for the residues that serve as the distal ligands for the heme located in the middle portion of the QPO sequence and corresponds to the N-terminal heme (low-potential heme) of BCCP (Yamada et al., 2007). Homologues of the qpo gene are widely distributed among many gram-negative bacteria, including Haemophils ducreii, Bacteroides fragilis, and Escherichia coli. Because BCCP and QPO are phylogenetically similar, we grouped them in a single enzyme family designated the bacterial multiheme peroxidase family (Takashima et al., 2007).
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