pyochelin and anguibactin

The regulatory logic of siderophore biosynthetic genes in bacteria involves the universal repressor Fur, which acts together with iron as a negative regulator. However in other bacteria, in addition to the Fur-mediated mechanism of regulation, there is a concurrent positive regulation of iron transport and siderophore biosynthetic genes that occurs under conditions of iron deprivation. Despite these regulatory differences the mechanisms of siderophore biosynthesis follow the same fundamental enzymatic logic, which involves a series of elongating acyl-S-enzyme intermediates on multimodular protein assembly lines: nonribosomal peptide synthetases (NRPS). A substantial variety of siderophore structures are produced from similar NRPS assembly lines, and variation can come in the choice of the phenolic acid selected as the N-cap, the tailoring of amino acid residues during chain elongation, the mode of chain termination, and the nature of the capturing nucleophile of the siderophore acyl chain being released. Of course the specific parts that get assembled in a given bacterium may reflect a combination of the inventory of biosynthetic and tailoring gene clusters available. This modular assembly logic can account for all known siderophores. The ability to mix and match domains within modules and to swap modules themselves is likely to be an ongoing process in combinatorial biosynthesis. NRPS evolution will try out new combinations of chain initiation, elongation and tailoring, and termination steps, possibly by genetic exchange with other microorganisms and/or within the same bacterium, to create new variants of iron-chelating siderophores that can fit a particular niche for the producer bacterium.

Topics: Amino Acid Sequence; Bacteria; Catechols; Enterobactin; Genes, Bacterial; Molecular Sequence Data; Molecular Structure; Oxazoles; Peptides; Phenols; Sequence Homology, Amino Acid; Siderophores; Thiazoles

Clinical isolates of Yersinia enterocolitca, which belong to mouse-lethal serotypes, produce the siderophore yersiniophore. Siderophore production was shown to be iron regulated and to reach maximum production in late log phase. Yersiniophore is a fluorescent siderophore with maximum excitation at 270 nm and a major emission peak at 428 nm. Absorption maxima were seen at 210 and 250 nm with a low broad peak from 280 to 320 nm. Purification of unchelated yersiniophore for structural analysis was made difficult by low yields (1-2 mg mg-1), and susceptibility to acid hydrolysis, oxidation and possibly polymerization. Yersinophore was therefore purified as an Al3+ chelate, which was found to be stable in solution for several weeks. To purify Al(3+)-yersinophore, unchelated yersiniophore was first extracted from culture supernatants with dichloromethane, concentrated by rotary evaporation and adsorbed to a DEAE-sephacel column. Al(3+)-yersiniophore was eluted with 0.01 M AlCl3 and further purified by HPLC. The structure was established by a combination of elemental analysis, high resolution mass spectrometry and two-dimensional NMR experiments. Yersiniophore is a phenolate-thiazole siderophore with the formula C21H24N3O4S3Al and a molecular weight of 505.07404 when chelated to Al3+. The structure of yersiniophore was determined to be closely related to the structures of pyochelin, produced by Pseudomonas aeruginosa, and anguibactin, produced by Vibrio anguillarum.

Topics: Aluminum; Animals; Chromatography, High Pressure Liquid; Chromatography, Ion Exchange; Feces; Humans; Magnetic Resonance Spectroscopy; Mass Spectrometry; Mice; Peptides; Phenols; Pseudomonas aeruginosa; Siderophores; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Structure-Activity Relationship; Thiazoles; Vibrio; Yersinia enterocolitica