Product Code Database
PyoverdinesFor the purposes of this page, pyoverdine will generally refer (unless otherwise noted) to the pyoverdine produced by Pseudomonas aeruginosa strain PAO1. It has been subjected to the most extensive study and can be considered the prototypical siderophore. (alternatively, and less commonly, spelled as pyoverdins) are fluorescence siderophores produced by certain Pseudomonadaceae. Pyoverdines are important , and are required for pathogenesis in many biological models of infection. Their contributions to bacterial pathogenesis include providing a crucial nutrient (i.e., iron), regulation of other virulence factors (including exotoxin A and the protease PrpL), supporting the formation of , and are increasingly recognized for having toxin themselves.
Pyoverdines have also been investigated as "Trojan Horse" molecules for the delivery of to otherwise resistant bacterial strains, as chelation that can be used for bioremediation of heavy metals, and as fluorescent reporters used to assay for the presence of iron and potentially other metals.
Due to their bridging the gaps between , iron metabolism, and fluorescence, pyoverdines have piqued the curiosity of scientists around the world for over 100 years.
In addition to this role, pyoverdine has a number of other functions, including regulating virulence, limiting the growth of other bacterial species (and serving as a sort of antimicrobial) by limiting iron availability, and sequestering other metals and preventing their toxicity.
The core is modified by the addition of an amino acid chain composed of 6-14 amino acids. The chain of amino acids is built onto the chromophore core, and is synthesized via non-ribosomal peptide synthesis. As is common for non-ribsosomally synthesized peptides, pyoverdine frequently includes D-form amino acids and non-standard amino acids, such as Ornithine. The peptide chain may also be partially (or completely) cyclized. This peptide chain provides the other four aspects of the denticity interaction, usually through Hydroxamic acid and/or hydroxycarboxylate groups. This portion of the molecule is also crucial for interaction with the ferripyoverdine receptor (FpvA) that allows ferripyoverdine to be imported into the cell. The peptide chain produced by a given strain of Pseudomonadaceae is currently thought to be invariant.
Little is known about the particular function or importance of the ketoacid side chain, but it is well known that pyoverdine molecules with different ketoacids (congeners) co-exist. Ketoacids that have been observed include succinic acid/succinimide, glutamic acid, glutaric acid, malic acid/malamide, and α-ketoglutarate.
| +Structure of the peptide backbone in various fluorescent Pseudomonas strains. Amino acid three-letter codes are used, along with Q=chromophore, DXxx=D-amino acid, aThr=allo-threonine, c=cyclic structure, cOHOrn=cyclo-hydroxyornithine, Dab=diaminobutyric acid, Ac=Acetyl, Fo=formyl OH=hydroxyl | ||
| P. aeruginosa | ATCC15692 (PAO1) | Q-DSer-Arg-DSer-FoOHOrn-c(Lys-FoOHOrn-Thr-Thr) |
| P. aeruginosa | ATCC27853 | Q-DSer-FoOHDOrn-Orn-Gly-aDThr-Ser-cOHOrn |
| P. aeruginosa | Pa6 | Q-DSer-Dab-FoOHOrn-Gln-DGln-FoOHDOrn-Gly |
| P. chlororaphis | ATCC9446 | Q-DSer-Lys-Gly-FoOHOrn-c(Lys-FoOHDOrn-Ser) |
| P. fluorescens bv.I | ATCC13525 | Q-DSer-Lys-Gly-FoOHOrn-c(Lys-FoOHDOrn-Ser) |
| P. fluorescens bv.I | 9AW | Q-DSer-Lys-OHHis-aDThr-Ser-cOHOrn |
| P. fluorescens bv.III | ATCC17400 | Q-DAla-DLys-Gly-Gly-OHAsp-DGln/Dab-Ser-DAla-cOHOrn |
| P. fluorescens bv.V | 51W | Q-DAla-DLys-Gly-Gly-OHDAsp-DGln-DSer-Ala-Gly-aDThr-cOHOrn |
| P. fluorescens bv.V | 1W | Q-DSer-Lys-Gly-FoOHOrn-c(Lys-FoOHDOrn-Ser) |
| P. fluorescens bv.V | 10CW | Q-DSer-Lys-Gly-FoOHOrn-c(Lys-FoOHDOrn-Ser) |
| P. fluorescens bv.VI | PL7 | Q-DSer-AcOHDOrn-Ala-Gly-aDThr-Ala-cOHOrn |
| P. fluorescens bv.VI | PL8 | Q-DLys-AcOHDOrn-Ala-Gly-aDThr-Ser-cOHOrn |
| P. fluorescens | 1.3 | Q-DAla-DLys-Gly-Gly-OHAsp-DGln/Dab-Gly-Ser-cOHOrn |
| P. fluorescens | 18.1 | Q-DSer-Lys-Gly-FoOHOrn-Ser-DSer-Gly-c(Lys-FoOHDOrn-Ser) |
| P. fluorescens | CCM 2798 | Q-Ser-Dab-Gly-Ser-OHDAsp-Ala-Gly-DAla-Gly-cOHOrn |
| P. fluorescens | CFBP 2392 | Q-DLys-AcOHDOrn-Gly-aDThr-Thr-Gln-Gly-DSer-cOHOrn |
| P. fluorescens | CHA0 | Q-Asp-FoOHDOrn-Lys-c(Thr-Ala-Ala-FoOHDOrn-Lys) |
| P. putida bv. B | 9BW | Q-DSer-Lys-OHHis-aDThr-Ser-cOHOrn |
| P. putida | CFBP 2461 | Q-Asp-Lys-OHDAsp-Ser-aDThr-Ala-Thr-DLys-cOHOrn |
| P. tolaasii | NCPPB 2192 | Q-DSer-Lys-Ser-DSer-Thr-Ser-AcOHOrn-Thr-DSer-cOHDOrn |
Pyoverdine coordinates a denticity (i.e., six-part) chelation of iron that involves six different oxygen atoms (2 from the dihyodroxyquinoline core and 2 from each of 2 different amino acids in the backbone). This results in a very tightly coordinated octahedral complex that efficiently prevents the ingress of water or other materials that may disrupt binding. Typically, ferric is removed from pyoverdine by redox to the ferrous state, for which pyoverdine has a much lower (i.e., 10 M) avidity. This allows for the non-destructive removal of iron from pyoverdine. After reduction, the iron is "handed off" to other carriers that have increased affinity for ferrous iron, while the apopyoverdine is re-exported for continued use.
Pyoverdine is structurally similar to azobactin, from Azotobacter vinelandii, except that the latter possesses an extra urea ring.
Pyoverdine biosynthesis seems to be largely regulated through the activity of the alternate sigma factor PvdS which, in turn, is regulated both by the Fur system and by the intracellular sequestration of PvdS at the cell membrane and away from the nucleoid by the repressor FpvI.
Despite significant investigation, relatively little is known about the biosynthesis of pyoverdine. For example, It remains unclear whether the biosynthesis of pyoverdine takes place as individual components (i.e., the core, the peptide chain, and the ketoacid) or if the core and the other parts are condensed as a beginning molecule (possibly by the PvdL protein) and then modified by other enzymes afterward. For reasons that remain unclear, pyoverdine biosynthesis is strongly inhibited by the anti-cancer therapeutic fluorouracil, particularly through its ability to disrupt RNA metabolism. Although production of pyoverdines varies from strain to strain, fluorescent Pseudomonas species have been shown to produce between 200 and 500 mg/L when grown in iron-depleted conditions.
A separate report suggests that pvcABCD may be responsible for the synthesis of paerucumarin (a pseudoverdine-related molecule) instead, and claims that loss of activity in the locus has no effect on pyoverdine production. In addition, some fluorescent Pseudomonads lack apparent homologs of these genes, further calling into question whether this is the function of these genes.
This is consistent with reports that pvdL combines coenzyme A to a myristic acid acid moiety, then adds a glutamate, tyrosine, and L-2,4-diaminobutyric acid (DAB). An alternate biosynthetic pathway suggests that pvdL incorporates glutamate, 2,4,5-trihydroxyphenylalanine and L-2,4-daminobutyric acid instead. This latter is supported by the identification of incorporation of a radiolabeled tyrosine into either pyoverdine or pseudoverdine.
This discrepancy remains unresolved.
As noted above, pyoverdine contributes in several fashions to general virulence, including regulating the production of itself, exotoxin A (which stalls translation), and the protease PrpL. There is also evidence that, although not essential for its formation, pyoverdine contributes to the production and development of biofilms that are important for virulence.
Finally, pyoverdine is associated with several types of toxicity in its own right. In 2001, Albesa and colleagues reported that pyoverdine purified from a strain of P. fluorescens exhibited profound cytotoxicity to mammalian and that this effect was at least partially dependent upon reactive oxygen species. Later, Kirienko and colleagues determined that pyoverdine is both necessary and sufficient for killing C. elegans, that enters host cells, destabilizes mitochondrial dynamics, and induces a hypoxic response. Exposure triggers a response that is consistent with hypoxia that depends on the HIF-1 protein, suggesting that the host perceives a condition where it lacks the molecular tools for generating ATP glycolysis.
In P. aeruginosa, pyoverdine non-producing “cheat” bacteria have been shown to i) evolve readily from a producing ancestor; and ii) outcompete cooperating strains in mixed culture in a density- and frequency-dependent manner. Since pyoverdine usage relies on passive diffusion and pyoverdine production is metabolically costly, environmental conditions are known to influence the likelihood of successful exploitation. The competitive advantage of pyoverdine non-producers over producers in mixed culture was shown to be maximized when environments are well-mixed and molecules diffuse readily (low spatial structure) and when the costs and benefits of pyoverdine production are high, i.e. when iron is strongly limited. Most studies on pyoverdine cooperation and cheating have been conducted using clinical isolates, but siderophore exploitation was recently also demonstrated in natural Pseudomonas isolates from non-clinical samples.
Pseudoverdine is relatively similar to pyoverdine in its fluorescence and other spectroscopy properties, and its ability to chelate ferric iron, albeit at much lower affinity. Unlike pyoverdine, it is incapable of active transport iron into cells, likely due to the absence of the peptide chain. Another dissimilarity is that pseudoverdine does not appear to be regulated by the same processes as pyoverdine.
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