Two microarray studies, however, reported increased transcript abundances for many of the putative iron transporters when iron was complexed with dipyridyl [35] or sequestered by iron-binding proteins in blood plasma [33].

2D gel analysis has known limitations pertaining to protein detection sensitivity and the resolution of hydrophobic IM-localized proteins, e.g. many nutrient transporters. Except Ysu subunits, unproven iron transporters were also not profiled employing a peptide-based LC-MS/MS analysis approach with Y. pestis lysates [47, 65]. These lysates were derived from iron-replete growth conditions. Only functional iron transporters are presented in the schematic of Figure 5 and appear to follow a hierarchy of importance in the order of Ybt, Yfe (each important for virulence in a bubonic plague model), Yfu and Yiu [15]. The delivery of Fe3+ or Fe2+ from learn more the extracellular milieu to periplasmic binding proteins of the ABC transporters

Yfe, Yfu and Yiu is unclear, although a YiuR MI-503 surface receptor was expressed according to our data. The Hmu transporter acquires heme from blood plasma proteins such as myoglobin, hemoglobin and hemopexin [16]. Three Fe2+ transport systems (EfeUOB, Y2368-Y2370 and FeoAB, Figure 5) were shown to be functional in either Y. pestis [17] or other bacteria [66–68]. We identified the subunits EfeO and Y2368 as periplasmic proteins, and their abundance increases in iron-deficient cells appeared to be moderately temperature-dependent. There is no evidence to date for their regulation by Fur. FeoB was recently identified in Y. pestis membrane proteome surveys [47, 65]. A protein highly abundant in membrane fractions of iron-depleted Y. pestis cells but not characterized in the context of iron transport was the orphan TonB-dependent OM receptor Y0850. The protein is a candidate for Fur regulation and the contribution to iron uptake, but its exact function remains to be elucidated. A conserved

Fur box upstream of the gene and sequence similarity of Y0850 to Bordetella bronchiseptica BfrA and Campylobacter coli CfrA [69, 70] were established. Our proteomic surveys did not support the activation of specific iron uptake pathways at only one of the physiologically relevant diglyceride temperatures. Based on multivariate transcriptional profiling data for Y. pestis (28°C vs. 37°C, iron-supplemented cell growth vs. iron sequestration in plasma), Carniel et al. [33] suggested that the Ybt system and the TonB protein are of particular importance for iron acquisition at 37°C. Fe-S cluster biosynthesis and energy metabolism in iron-starved Y. pestis Growth of iron-depleted Y. pestis cells was arrested at an OD600 of ~0.8, indicative of the inability of iron-dependent enzymes to perform essential metabolic functions. In addition to the already discussed impact of iron depletion on oxidative stress response enzymes and aconitases, we explored how Fe-S cluster assembly systems and other energy metabolism enzymes were affected.