Cleavage of a putative metal permease in Chlamydia trachomatis yields an iron-dependent transcriptional repressor

Abstract

The regulation of iron homeostasis is essential for most organisms, because iron is required for a variety of conserved biochemical processes, yet can be toxic at high concentrations. Upon experiencing iron starvation in vitro, the obligate intracellular human pathogen Chlamydia trachomatis exhibits elevated expression of a putative iron-transport system encoded by the ytg operon. The third component of the ytg operon, CT069 (YtgCR), encodes a protein with two distinct domains: a membrane-anchored metal ion permease and a diphtheria toxin repressor (DtxR)-like transcriptional repressor. In this report, we demonstrate that the C-terminal domain of CT069 (YtgR) serves as an iron-dependent autorepressor of the ytg operon. Moreover, the nascent full-length metal permease-transcriptional repressor protein was processed during the course of infection, and heterologously when expressed in Escherichia coli. The products produced by heterologous cleavage in E. coli were functional in the repression of a reporter gene downstream of a putative YtgR operator. We report a bona fide mechanism of iron-dependent regulation of transcription in Chlamydia. Moreover, the unusual membrane permease-DNA-binding polypeptide fusion configuration was found in several bacteria. Therefore, the DNA-binding capability and liberation of the YtgR domain from a membrane-anchored permease in C. trachomatis could represent a previously uncharacterized mechanism for prokaryotic regulation of iron-homeostasis.ron is an essential micronutrient for nearly all organisms, with its redox capability being both beneficial and harmful to the organism, because of iron readily catalyzing the formation of toxic free radicals via the Haber-Weiss reaction (1). Thus, both eukaryotes and prokaryotes, alike, have evolved regulatory networks for the tight control of intracellular iron homeostasis.In prokaryotes, these regulatory networks are usually controlled through metal-dependent DNA-binding proteins. Two of the best-characterized metal-dependent transcriptional regulators are ferric uptake regulator (Fur) in Escherichia coli and diphtheria toxin repressor (DtxR) in Corynebacterium diphtheriae. Although nonhomologous and structurally distinct, both families of transcriptional repressors function similarly, in that the presence of a cognate metal cofactor activates DNA-binding activity (2). Homodimers of the metal-activated proteins recognize specific cis-regulatory elements that are often located proximally to the promoter operating regions of the regulated gene, effectively blocking RNA polymerase initiation of transcription (3, 4).Chlamydia trachomatis is an obligate, intracellular human pathogen that is responsible for the leading cause of bacterial sexually transmitted infection (5, 6) and infection-derived blindness (7) worldwide. The chlamydial requirement for iron is well established, because iron restriction forces Chlamydia into an alternative persistent growth mode distinguished by abnormal morphology (8-10) and altered transcriptional profile of hall...

The iron-dependent repressor YtgR regulates the tryptophan salvage pathway through a bipartite mechanism of transcriptional control inChlamydia trachomatis

“…We then sequenced the 478 ligated inserts and BLASTed the sequences against the C. trachomatis L2 434/Bu 479 genome to identify the location of the 5'-most nucleotides ( Figure 4C). These data are 480 displayed as a statistical approximation of the genomic regions most likely to be 481 galactosidase activity (p = 0.03868) consistent with its previously reported auto-588 regulation of this promoter (Thompson et al, 2012). 589…”

“…Importantly, Chlamydia presumably acquire iron via vesicular 127 interactions between the chlamydial inclusion and slow-recycling transferrin (Tf)-128 containing endosomes (Ouellette & Carabeo, 2010). IFN-g is known to down-regulate 129 transferrin receptor (TfR) expression in both monocytes and epithelial cells with 130 YtgC (CTL0325) open reading frame (ORF) encodes a N-terminal permease domain 138 fused to a C-terminal DtxR-like repressor domain, annotated YtgR (Akers,HoDac,139 Lathrop, & Tan, 2011; Thompson, Nicod, Malcolm, Grieshaber, & Carabeo, 2012). YtgR 140 is cleaved from the permease domain during infection and functions as an iron-141 dependent transcriptional repressor to autoregulate the expression of its own operon 142 (Thompson et al, 2012).…”

“…IFN-g is known to down-regulate 129 transferrin receptor (TfR) expression in both monocytes and epithelial cells with 130 YtgC (CTL0325) open reading frame (ORF) encodes a N-terminal permease domain 138 fused to a C-terminal DtxR-like repressor domain, annotated YtgR (Akers,HoDac,139 Lathrop, & Tan, 2011; Thompson, Nicod, Malcolm, Grieshaber, & Carabeo, 2012). YtgR 140 is cleaved from the permease domain during infection and functions as an iron-141 dependent transcriptional repressor to autoregulate the expression of its own operon 142 (Thompson et al, 2012). YtgR represents the only identified iron-dependent 143 transcriptional regulator in Chlamydia.…”

Manganese uptake and streptococcal virulence

“…Notably, the precise physiological role of T. pallidum TroA remains unclear, while it has been implicated in potentially mediating Mn 2+ , Fe 2+ and/or Zn 2+ uptake (Desrosiers et al 2007; Hazlett et al 2003). Similarly, YtgA from Chlamydia trachomatis has been associated with Fe 2+ , Fe 3+ and/or Zn 2+ transport processes, although a direct physiological role has not been shown (Akers et al 2011; Miller et al 2009; Thompson et al 2012). One of the very few functional roles that have been definitively established within this subgroup is for TroA from S. suis and its role in physiological Mn 2+ acquisition (Wichgers Schreur et al 2011).…”

Phage Conversion and the Role of Bacteriophage and Host Functions in Regulation of Diphtheria Toxin Production by Corynebacterium diphtheriae

“…Close homologs of DtxR are widely distributed among Corynebacterium spp. (Oram et al 2004;Brune et al 2006), and more distantly related homologs of DtxR have been identified in numerous bacterial genera (particularly among Gram-positive and acid-fast bacteria), including but not limited to: Brevibacterium lactofermentum (Oguiza et al 1995), Chlamydia trachomatis (Thompson et al 2012), Mycobacterium smegmatis (Dussurget et al 1996), Mycobacterium tuberculosis , Staphylococcus aureus (Hill et al 1998), Staphylococcus epidermidis (Hill et al 1998), Streptomyces lividans (Gunter-Seeboth and Schupp 1995), Streptomyces pilosus (Gunter-Seeboth and Schupp 1995), and Treponema pallidum (Hardham et al 1997). The iron-dependent regulator (IdeR) from M. tuberculosis was the first member of the DtxR family shown to be a dual regulator that can repress transcription at some promoters that it regulates and activate transcription at other promoters that it regulates (Gold et al 2001).…”