Metabolite-driven Regulation of Heme Uptake by the Biliverdin IXβ/δ-Selective Heme Oxygenase (HemO) of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa acquires extracellular heme via the Phu (Pseudomonas heme uptake) and Has (heme assimilation system) systems. We have previously shown the catalytic actions of heme oxygenase (HemO) along with the cytoplasmic heme transport protein PhuS control heme flux into the cell. To further investigate the role of the PhuS-HemO couple in modulating heme uptake, we have characterized two HemO variants, one that is catalytically inactive (HemO H26A/K34A/K132A or HemOin) and one that has altered regioselectivity (HemO N19K/K34A/F117Y/K132A or HemOα), producing biliverdin IXα (BVIXα). HemOα similar to wild type was able to interact and acquire heme from holo-PhuS. In contrast, the HemOin variant did not interact with holo-PhuS and showed no enzymatic activity. Complementation of a hemO deletion strain with the hemOin or hemOα variants in combination with [(13)C]heme isotopic labeling experiments revealed that the absence of BVIXβ and BVIXδ leads to a decrease in extracellular levels of hemophore HasA. We propose BVIXβ and/or BVIXδ transcriptionally or post-transcriptionally regulates HasA. Thus, coupling the PhuS-dependent flux of heme through HemO to feedback regulation of the cell surface signaling system through HasA allows P. aeruginosa to rapidly respond to fluctuating extracellular heme levels independent of the iron status of the cell.

Contributions of the Heme Coordinating Ligands of thePseudomonas aeruginosaOuter Membrane Receptor HasR to Extracellular Heme Sensing and Transport

“…As previously reported supplementation of PAO1 WT with 1 µM heme after an initial decrease in mRNA levels we observed an increase in hasR mRNA levels over time as extracellular HasAp levels accumulate ( Fig 7A). The hasAp mRNA profiles mirror those of hasR, however, as previously reported the relative mRNA levels are greater than hasR due to increased mRNA stability following processing of the hasRAp transcript ( Fig 7B) (16). Western blot analysis of HasR and HasAp protein levels are consistent with the respective mRNA profiles (Fig 8).…”

“…HemO catalyzes the oxidative cleavage of heme to release CO, iron and the heme metabolites biliverdin IXβ (BVIXβ) and -IXδ (BVIXδ) (17). In addition to hemedependent transcriptional activation of the Has system, the hasAp transcript is subject to post-transcriptional regulation by the heme metabolites BVIXb and/or BVIXδ (16).…”

“…The significance of heme sensing and uptake in P. aeruginosa pathogenesis is evident in the fact that clinical isolates from patients with chronic lung infection have adapted to utilize heme while decreasing pyoverdine biosynthesis (21). The Has system has several layers of transcriptional and posttranscriptional regulation that allows the bacteria to rapidly fine tune its response to changes in the host environment (15,16). In an attempt to dissect the mechanism of heme signaling and transport by the P. aeruginosa Has system, we have employed site directed mutagenesis, allelic exchange, qPCR, immunoblotting and 13 C-heme uptake studies to determine the contributions of the heme coordinating ligands of HasR (Fig.…”

The Pseudomonas aeruginosa PrrF Small RNAs Regulate Iron Homeostasis during Acute Murine Lung Infection

“…Standard curves were produced for each primer-probe set listed in Table S1 in the supplemental material by analyzing cDNA generated from serial dilutions of RNA and used to determine relative amounts of the RNAs, as described previously (22). Relative RNA levels were then normalized to the levels of the oprF mRNA as previously described (22,59,60) for aerobic expression studies or to the omlA level as previously described (21) for microaerobic expression studies. The expression of each of these genes was constant under these respective conditions (Fig.…”

Regulation of Pseudomonas aeruginosa Virulence by Distinct Iron Sources

“…Notably, the biliverdin isomer pattern produced by P. aeruginosa HemO is unique in that the heme molecule is cleaved at the β or δ carbon of the porphyrin ring, in contrast to cleavage at the α carbon mediated by all other characterized heme oxygenases [66]. The unique biliverdin isomer pattern produced by P. aeruginosa HemO was recently shown to allow for the positive feedback regulation of HasA hemophore production [67]. Combined, these studies indicate that the heme acquisition pathway of P. aeruginosa is capable of regulating gene expression by at least two distinct mechanisms.…”