Abstract
FeoB is an atypical transporter that has been shown to exclusively mediate ferrous ion transport in some bacteria. Unusually the genome of the periodontal pathogen Porphyromonas gingivalis has two genes (feoB1 and feoB2) encoding FeoB homologs, both of which are expressed in bicistronic operons. Kinetic analysis of ferrous ion transport by P. gingivalis W50 revealed the presence of a single, high affinity system with a K(t) of 0.31 microM. FeoB1 was found to be solely responsible for this transport as energized cells of the isogenic FeoB1 mutant (W50FB1) did not transport radiolabeled iron, while the isogenic FeoB2 mutant (W50FB2) transported radiolabeled iron at a rate similar to wild type. This was reflected in the iron content of W50FB1 grown in iron excess conditions which was approximately half that of the wild type and W50FB2. The W50FB1 mutant had increased sensitivity to both oxygen and hydrogen peroxide and was avirulent in an animal model of infection whereas W50FB2 exhibited the same virulence as the wild type. Analysis of manganous ion uptake using inductively coupled plasma-mass spectrometry revealed a greater than 3-fold decrease in intracellular manganese accumulation in W50FB2 which was also unable to grow in manganese-limited media. The protein co-expressed with FeoB2 appears to be a novel FeoA-MntR fusion protein that exhibits homology to a manganese-responsive, DNA-binding metalloregulatory protein. These results indicate that FeoB2 is not involved in iron transport but plays a novel role in manganese transport.
Highlights
The transition metal, iron, is an essential growth requirement for most bacteria due to its redox activity and role in many vital cellular reactions
The cytoplasmic N-terminal domain of FeoB proteins has recently been shown to act as a GTPase and not to function as an ATPase as had originally been proposed [30, 31]. Both P. gingivalis FeoB1 and FeoB2 contain four of the five characteristic G protein motifs required for GTPase activity that are found in other bacterial FeoBs (Fig. 1; Ref. 30)
The two putative P. gingivalis FeoB proteins have a high degree of similarity; the main region of sequence disparity is the N-terminal region of FeoB1 that has significant similarity to E. coli FeoA (Fig. 2) suggesting that P. gingivalis FeoB1 is a FeoA/B fusion protein
Summary
The protein co-expressed with FeoB2 appears to be a novel FeoA-MntR fusion protein that exhibits homology to a manganese-responsive, DNA-binding metalloregulatory protein. These results indicate that FeoB2 is not involved in iron transport but plays a novel role in manganese transport. The transition metal, iron, is an essential growth requirement for most bacteria due to its redox activity and role in many vital cellular reactions. FeoB was shown to be the only ferrous ion transport system in both of these bacteria using isogenic mutants in radiolabeled iron uptake assays. We have characterized FeoB1 as the ferrous ion transporter, which plays an important role in the virulence of P. gingivalis in a murine model of infection.
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