An Escherichia coli cyoE gene homologue in thermophilic Bacillus PS3 encodes a thermotolerant heme O synthase

Abstract

The cyoE gene of the Escherichia coli bo-type quinol oxidase operon (cyoABCDE) has been previously shown to encode heme O synthase. To demonstrate a catalytic role of a cyoE homologue (the caaE gene) in the gene cluster for caa3-type cytochrome c oxidase of thermophilic Bacillus PS3, we have carried out genetic complementation analysis using the chimeric operon cyoABCD-caaE and heme O synthase assay using the CaaE-overproduced E. coli membranes. We found that the caaE gene encodes a thermotolerant heine O synthase which provides an intermediate for heme A biosynthesis.

Expression of the Escherichia coli cyo operon in Paracoccus denitrificans results in a fully active quinol oxidase of unexpected heme composition

“…In this study we address the question of heme composition of the E. coli oxidase when expressed in a P. denitrificans host, and show that the purified enzyme exhibits a ba 3 heme composition. In contrast to the previously described non‐functional quinol oxidase species with a b ‐type heme in the binuclear center [3, 4, 9, 10]this enzyme retains its electron transfer competence at wild‐type level.…”

“…With the exception of cbb 3 ‐type cytochrome c oxidases, all available evidence indicates that heme b is not able to sustain enzymatic activity of heme‐copper oxidases when incorporated into the high‐spin site. This has been studied in detail for the quinol oxidases of E. coli [3, 4, 9]and P. denitrificans [10]. The close to wild‐type activity observed for the Cyo oxidase purified from P. denitrificans therefore excludes the presence of heme b as a constituent of the high‐spin site of this particular enzyme complex.…”

TheBacillus subtilis ctaBparalogue,yjdK, can complement the heme A synthesis deficiency of a CtaB-deficient mutant

“…Mutants lacking CtaA and/or CtaB contain no detectable heme A [2]. CtaB has been shown to be a heme O synthase (protoheme IX hydroxyethylfarnesyltransferase) ([5], our unpublished data), very similar to its well studied Escherichia coli homologue, CyoE [6,7]. CtaA is involved in the conversion of heme O to heme A and contains heme B as a prosthetic group [4,8].…”

The Bacillus subtilis ctaB paralogue, yjdK, can complement the heme A synthesis deficiency of a CtaB-deficient mutant

“…Mutants lacking CtaA and/or CtaB contain no detect-able heme A [2]. CtaB has been shown to be a heme O synthase (protoheme IX hydroxyethylfarnesyltransferase) ( [5], our unpublished data), very similar to its well studied Escherichia coli homologue, CyoE [6,7]. CtaA is involved in the conversion of heme O to heme A and contains heme B as a prosthetic group [4,8].…”