Modular Fluorescent-Labeled Siderophore Analogues

Abstract

Biomimetic analogues 1 of the microbial siderophore (iron carrier) ferrichrome were labeled via piperazine with various fluorescent markers at a site not interfering with iron binding or receptor recognition (compounds 10-12). These iron carriers were built from a tetrahedral carbon symmetrically extended with three strands, each containing an amino acid (G = glycyl, A = alanyl, L = leucyl and P = phenylalanyl) and terminated by a hydroxamic acid, which together define an octahedral iron-binding domain. A fourth exogenous strand provided the site for connecting various fluorescent markers via a short bifunctional linker. Iron(III) titrations, along with fluorescence spectroscopy, generated quenching of fluorescence emission of some of the probes used. The quenching process fits the Perrin model which reinforces the intramolecular quenching process, postulated previously.1 All tested compounds, regardless of their probe size, polarity, or the linker binding them to the siderophore analogue, promote growth of Pseudomonas putida with the same efficacy as the nonlabeled analogues 1, with the added benefit of signaling microbial activity by fluorescence emission. All G derivatives of compounds 10-12 were found to parallel the behavior of natural ferrichrome, whereas A derivatives mediated only a modest iron(III) uptake by P. putida. Incubation of various Pseudomonas strains with iron(III)-loaded G derivatives resulted in the build-up of the labels' fluorescence in the culture medium to a much larger extent than from the corresponding A derivatives. The fluorescence buildup corresponds to iron utilization by the cells and the release of the fluorescent labeled desferrisiderophore from the cell to the media. The fact that the microbial activity of these compounds is not altered by attachment of various fluorescent markers via a bifunctional linker proposes their application as diagnostic tools for detecting and identifying pathogenic microorganisms.

Identification of a Candida albicans Ferrichrome Transporter and Its Characterization by Expression inSaccharomyces cerevisiae

“…genetically characterized S. cerevisiae) offers an opportunity to study the recognition properties of the pathogen's siderophore transporter. This may help in the development of siderophore analogs with antimicrobial properties (32,33). While this development may be done empirically by screening analogs, knowledge of the mechanism of siderophore-iron uptake would accelerate this approach.…”

Siderophores for molecular imaging applications

“…Table 1 summarizes applications of siderophores as imaging agents. They can be prepared either by the introduction of appropriate radiometal to the natural (iron-)siderophore complex via the exchange of iron or artificially by the modification of natural siderophore with a chromophore suitable for optical imaging [31][32][33][34]. Already in the 1970s and 1980s, first investigations of radiolabelled siderophores, including desferrioxamine (DFO), were already reported with gamma-emitting radionuclides- 67 Ga and 111 In [35][36][37][38].…”

“…Several groups have developed strategies of synthesizing siderophore-chromophore conjugates for optical imaging [31][32][33][55][56][57][58]. Siderophores (e.g.…”

“…Pseudomonas spp.) [31,32,58] and fungi (Ustilago maydis, Saccharomyces cerevisiae, Candida albicans and Rhizzopus arrhizus) [33,55,57]. The microbial activity was not altered by the attachment of various functionalities and fluorescent siderophore analogues became invaluable tools in the investigation of molecular mechanisms involved in microbial iron transport and acquisition.…”

Synthesis and Ionophoric Properties of Crown Ether Capped with a Convergent Hydroxamic Acid Function

“…3 In particular, hydroxamic acid functions are employed frequently in many natural and synthetic ionophore systems and exhibited very unique binding behaviors toward some transition metal ions. [4][5][6][7] Meanwhile, in many of the designed supramolecular systems, obtaining a specific convergent orientation of particular ligating functions toward active site is highly desirable for selective and strong binding of targeted guests. For these purpose, U-shaped structural motif of Kemp's triacid is known to be very useful and resulted in the developments of many sophisticated supramolecular systems.…”