Regulation of Iron Transport inStreptococcus pneumoniaeby RitR, an Orphan Response Regulator

Abstract

RitR (formerly RR489) is an orphan two-component signal transduction response regulator in Streptococcus pneumoniae that has been shown to be required for lung pathogenicity. In the present study, by using the rough strain R800, inactivation of the orphan response regulator gene ritR by allele replacement reduced pathogenicity in a cyclophosphamide-treated mouse lung model but not in a thigh model, suggesting a role for RitR in regulation of tissue-specific virulence factors. Analysis of changes in genome-wide transcript mRNA levels associated with the inactivation of ritR compared to wild-type cells was performed by the use of high-density DNA microarrays. Genes with a change in transcript abundance associated with inactivation of ritR included piuB, encoding an Fe permease subunit, and piuA, encoding an Fe carrier-binding protein. In addition, a dpr ortholog, encoding an H 2 O 2 resistance protein that has been shown to reduce synthesis of reactive oxygen intermediates, was activated in the wild-type (ritR ؉ ) strain. Microarray experiments suggested that RitR represses Fe uptake in vitro by negatively regulating the Piu hemin-iron transport system. Footprinting experiments confirmed site-specific DNA-binding activity for RitR and identified three binding sites that partly overlap the ؉1 site for transcription initiation upstream of piuB. Transcripts belonging to other gene categories found to be differentially expressed in our array studies include those associated with (i) H 2 O 2 resistance, (ii) repair of DNA damage, (iii) sugar transport and capsule biosynthesis, and (iv) two-component signal transduction elements. These observations suggest that RitR is an important response regulator whose primary role is to maintain iron homeostasis in S. pneumoniae. The name ritR (repressor of iron transport) for the orphan response regulator gene, rr489, is proposed.

Serine/threonine/tyrosine phosphorylation regulates DNA binding of bacterial transcriptional regulators

“…It controls iron uptake and remediation of iron-catalysed reactive oxygen species (Throup et al, 2000;Ulijasz et al, 2004;Ong et al, 2013). RitR is annotated as a TCS RR, but because it does not possess a cognate HK it is called an orphan RR (Ulijasz et al, 2004).…”

Regulation of transcription by eukaryotic-like serine-threonine kinases and phosphatases in Gram-positive bacterial pathogens

“…Interestingly, some TCS system regulators have lost their conserved REC domain phospho-accepting aspartate residues and instead have evolved to accommodate more diverse inputs, effectively reverting back to a one-component unit. 55 To date, examples of these pseudo-response regulators have been few, however they are important in that most described thus far are required for infection in a variety of pathogens, including RitR from Streptococcus pneumoniae that regulates iron uptake and related responses to reactive oxygen species (ROS), 69 the general transcription regulator AmiR from Pseudomonas aeruginosa that regulates transcriptional termination, 68 and HP1043 from Helicobacter pylori and ChxR from Chlamydia trachomatis that regulate infection and virulence traits. 70,71 In this review we will concentrate on the emerging, alternative form of RNA synthesis control by eSTK phosphorylation of bacterial transcription factors, and the potential mechanistic consequences of these phospho-modifications.…”

“…153 Repressor of iron transport regulator (RitR) is a TCS-like response regulator in S. pneumoniae required for lung infection and responsible for iron uptake and remediation of iron-catalyzed ROS. 69,154,155 These actions are carried out in part by RitR-mediated repression of the pneumococcal iron uptake (Piu) transporter, and its simultaneous activation of bacterial ferritin (Dpr) and DNA repair enzymes under high oxygen tension (ref. 69 and unpublished data; Fig.…”

“…69,154,155 These actions are carried out in part by RitR-mediated repression of the pneumococcal iron uptake (Piu) transporter, and its simultaneous activation of bacterial ferritin (Dpr) and DNA repair enzymes under high oxygen tension (ref. 69 and unpublished data; Fig. 8).…”

“…Instead RitR is cotranscribed with 6-phosphogluconate dehydrogenase, a key enzyme in the pentose phosphate carbon utilization pathway. 69 Moreover, RitR is missing the conserved phosphorylated Asp residue within its REC domain. This posed the interesting question of how this transcription factor is regulated.…”