staphyloferrin-a and rhizoferrin

This paper briefly presents a review concerning the species which can arise when iron salts and citric acid are mixed together. The data commented on are required for a correct interpretation of the chemical processes which play a paramount role in biology and in the biological studies involving iron-citrate complexes.

Topics: Citrates; Citric Acid; Ferric Compounds; Ferrous Compounds; Iron; Models, Molecular; Ornithine; Oxidation-Reduction; Siderophores

During infection, Corynebacterium diphtheriae must compete with host iron-sequestering mechanisms for iron. C. diphtheriae can acquire iron by a siderophore-dependent iron-uptake pathway, by uptake and degradation of heme, or both. Previous studies showed that production of siderophore (corynebactin) by C. diphtheriae is repressed under high-iron growth conditions by the iron-activated diphtheria toxin repressor (DtxR) and that partially purified corynebactin fails to react in chemical assays for catecholate or hydroxamate compounds. In this study, we purified corynebactin from supernatants of low-iron cultures of the siderophore-overproducing, DtxR-negative mutant strain C. diphtheriae C7(β) ΔdtxR by sequential anion-exchange chromatography on AG1-X2 and Source 15Q resins, followed by reverse-phase high-performance liquid chromatography (RP-HPLC) on Zorbax C8 resin. The Chrome Azurol S (CAS) chemical assay for siderophores was used to detect and measure corynebactin during purification, and the biological activity of purified corynebactin was shown by its ability to promote growth and iron uptake in siderophore-deficient mutant strains of C. diphtheriae under iron-limiting conditions. Mass spectrometry and NMR analysis demonstrated that corynebactin has a novel structure, consisting of a central lysine residue linked through its α- and ε- amino groups by amide bonds to the terminal carboxyl groups of two different citrate residues. Corynebactin from C. diphtheriae is structurally related to staphyloferrin A from Staphylococcus aureus and rhizoferrin from Rhizopus microsporus in which d-ornithine or 1,4-diaminobutane, respectively, replaces the central lysine residue that is present in corynebactin.

Topics: Biological Transport; Citrates; Corynebacterium diphtheriae; Enterobactin; Ferric Compounds; Iron; Magnetic Resonance Spectroscopy; Ornithine; Siderophores; Spectrometry, Mass, Electrospray Ionization

Staphyloferrin A, the iron-transporting siderophore of Staphylococci, contains two citric acid residues linked to a D-ornithine backbone, having thus three chiral centers. While the chirality of the backbone can be determined after hydrolysis, the chirality of the two citryl residues can only be determined from the intact staphyloferrin A molecule by circular dichroism spectra. The chirality of the quarternary carbon atoms of citryl residues in fungal rhizoferrin and bacterial enantio-rhizoferrin have been determined previously to be R,R and S,S respectively. The present investigation shows that of the three chiral centers in staphyloferrin A, the citryl residues can be assigned an S,S-configuration by comparison with synthetic analogs, confirming a common chirality among the bacterial enantio-rhizoferrin and staphyloferrin A. This suggests that the bacterial carboxylates originate from a common biosynthetic pathway leading to an S,S-configuration, while the fungal rhizoferrin possessing an R,R-configuration must have a different biosynthetic origin. Growth promotion tests with staphylococci revealed that the S,S-configuration of staphyloferrin A and enantio-rhizoferrin enabled iron uptake, while the fungal rhizoferrin with R,R-configuration was not utilized.

Topics: Carbon; Circular Dichroism; Citrates; Citric Acid; Ferric Compounds; Hydrolysis; Iron; Models, Chemical; Ornithine; Siderophores; Spectrophotometry; Staphylococcus aureus; Stereoisomerism