BosR Is A Novel Fur Family Member Responsive to Copper and Regulating Copper Homeostasis in Borrelia burgdorferi

Abstract

The ferric uptake regulator (Fur) family of DNA-binding proteins represses and/or activates gene transcription via divalent metal ion-dependent signal sensing. The Borrelia burgdorferi Fur homologue, also known as Borrelia oxidative stress regulator (BosR), promotes spirochetal adaptation to the mammalian host by directly repressing the lipoproteins required for tick colonization and indirectly activating those required for establishing infection in the mammal. Here, we examined whether the DNA-binding activity of BosR was regulated by any of the four most prevalent transition metal ions in B. burgdorferi, Mn, Fe, Cu, and Zn. Our data indicated that in addition to a structural site occupied by Zn(II), BosR had two regulatory sites that could be occupied by Zn(II), Fe(II), or Cu(II) but not by Mn(II). While Fe(II) had no effect, Cu(II) and Zn(II) had a dose-dependent inhibitory effect on the BosR DNA-binding activity. Competition experiments indicated that Cu(II) had a higher affinity for BosR than Zn(II) or Fe(II). A BosR deficiency in B. burgdorferi resulted in a significant increase in the Cu level but no significant change in the levels of Mn, Fe, or Zn. These data suggest that Cu regulates BosR activity, and BosR in turn regulates Cu homeostasis in B. burgdorferi. While this regulatory paradigm is characteristic of the Fur family, BosR is the first one shown to be responsive to Cu(II), which may be an adaptation to the potentially high level of Cu present in the Lyme disease spirochete. IMPORTANCE Transition metal ions serve an essential role in the metabolism of all living organisms. Members of the ferric uptake regulator (Fur) family play critical roles in regulating the cellular homeostasis of transition metals in diverse bacteria, and their DNA-binding activity is often regulated by coordination of the cognate divalent metal ions. To date, regulators with metal ion specificity to Fe(II), Mn(II), Zn(II), and Ni(II) have all been described. In this study, we demonstrate that BosR, the sole Fur homologue in Borrelia burgdorferi, is responsive to Cu(II) and regulates Cu homeostasis in this bacterium, which may be an adaption to potentially Cu-rich milieu in the Lyme disease spirochete. This study has expanded the repertoire of the Fur family's metal ion specificity.

Borrelia Host Adaptation Protein (BadP) Is Required for the Colonization of a Mammalian Host by the Agent of Lyme Disease

“…It should be noted that there are higher-and lower-molecular-weight forms of BosR, reflecting the open and closed forms of this regulator, respectively. The levels of the highermolecular-weight form of BosR are associated with increased DNA-binding properties, notably, through coordination with transition metal ions, such as Zn 2ϩ /Cu 2ϩ , although the lower-molecular-weight form of BosR was readily detectable in the BadP mutants (52). The levels of several enzymes, such as superoxide dismutase A (SodA), lactate dehydrogenase (Ldh, BB0087), and PsgB, were similar in all strains and relatively comparable under conditions mimicking those in the midgut of both unfed and fed ticks.…”

“…Deletion of badP resulted in borrelial strains that were incapable of colonization of either immunocompetent C3H/ HeN or immunodeficient SCID mice, although the direct connection between the domains present in BadP to the regulation of the virulence attributes of B. burgdorferi is yet to be established. It is interesting to speculate that BadP plays a role as an enzyme in providing levels of select substrates/divalent cations that play a significant role in modulating BosR, a Zn 2ϩ /Cu 2ϩ -dependent regulator of RpoS, which is a major regulator of gene expression in B. burgdorferi (52).…”

The oligopeptide ABC transporter OppA4 negatively regulates the virulence factor OspC production of the Lyme disease pathogen

“…In addition, a Fur/PerR-like transcription factor, BosR, is also required for rpoS and ospC expression (Hyde et al, 2009; Ouyang et al, 2011; Ouyang et al, 2009; Wang et al, 2017). BosR is capable of binding to the promoter region of rpoS in vitro , the mechanism of how BosR is involved in activating rpoS transcription from a σ 54 promoter remains unclear (Hyde et al, 2009; Ouyang et al, 2011; Ouyang et al, 2009; Wang et al, 2017). Another transcription factor, BadR, directly represses rpoS expression (Miller et al, 2013; Ouyang and Zhou, 2015).…”

Borrelia burgdorferi spatiotemporal regulation of transcriptional regulator bosR and decorin binding protein during murine infection

“…Borrelia burgdorferi , a spirochetal bacterium, dynamically regulates gene expression to promote each stage of disease in the vector and mammalian host modulate disease and evade the immune response 2 , 6 – 8 . Changes in environmental cues, such as pH, temperature, O 2 , CO 2 , metals and osmotic stress, detected by B. burgdorferi result in differential presentation of lipoproteins on the outer membrane to promote adherence, invasion, and colonization 9 – 17 . Unknown host specific and tissue specific signals induce changes in gene expression that cannot be attributed to known environmental cues defined during in vitro cultivation 18 , 19 .…”

“…Metals have an important role in regulation and active state of BosR. Manganese, zinc, and copper have been shown to post-transcriptionally regulate BosR production 15,17 . Specifically, manganese represses and zinc promotes BosR synthesis 15 .…”