REY CARABEO, PhD
We are elucidating mechanisms of iron-dependent regulation of gene expression in Chlamydia. We identified an iron-dependent transcriptional repressor (YtgR) that exists as a fusion with an ABC transporter subunit (YtgC). This fusion protein precursor is cleaved to liberate the repressor domain. To determine gene targets of YtgR, we are utilizing a combination of transcriptomics of iron-starved chlamydiae and chromatin immunoprecipitation and sequencing (ChIP-seq) approach. A surprising finding is the YtgR regulation of transcription of the trp operon, specifically the open reading frames trpB and trpA from an alternative promoter. In this context, we determined that YtgR acts as a tryptophan-dependent trans-attenuator towards trpBA expression, possibly as part of the bacteria’s efforts in maintaining a fine-tuned trp operon expression in the absence of a discernible TrpL or TRAP-dependent attenuation mechanisms.
Finally, we extend our initial characterization of YtgR to include additional levels of regulation of its function. Like other iron-dependent transcriptional repressor, it requires iron for homodimerization and DNA binding. However, recent findings indicate that it is also regulated translationally and by proteolytic cleavage. The former involves a rare triple tryptophan motif that renders its translation sensitive to tryptophan levels, and this aspect of YtgR is related to its role as a trans-attenuator described above. Cleavage of the precursor protein liberates the YtgR repressor domain. We are currently investigating the identity of the protease(s) involved, the cleavage site, and the significance of this regulation on YtgR function and the chlamydial response to iron starvation.
- Pokorzynski ND, Hatch ND, Ouellette SP Carabeo RA. (2020) The iron-dependent repressor YtgR is a tryptophan-dependent attenuator of the trpRBA operon in Chlamydia trachomatis. Nature Communications doi: https://doi.org/10.1038/s41467-020-20181-5.
- Pokorzynski ND, Carabeo RA. (2019) A Bipartite Iron-Dependent Transcriptional Regulation of the Tryptophan Salvage Pathway in Chlamydia trachomatis. Elife. 8:e42295. doi: 10.7554/eLife.42295. doi: 10.7554/eLife.42295. PMID: 30938288.
- Pokorzynski ND, Thompson CC, Carabeo RA. (2017) Ironing Out the Unconventional Mechanisms of Iron Acquisition and Gene Regulation in Chlamydia. Front Cell Infect Microbiol. 2017 Sep 8;7:394. doi: 10.3389/fcimb.2017.00394. PMID: 28951853.
- Brinkworth AJ, Wildung MR, Carabeo RA. (2018) Genomewide Transcriptional Responses of Iron-Starved Chlamydia trachomatis Reveal Prioritization of Metabolic Precursor Synthesis over Protein Translation. mSystems. 3(1). pii: e00184-17. doi: 10.1128/mSystems.00184-17. PMID: 29468197.
- Thompson CC, Nicod SS, Malcolm DS, Grieshaber SS, Carabeo RA. (2012) Cleavage of a putative metal permease in Chlamydia trachomatis yields an iron-dependent transcriptional repressor. Proceedings of the National Academy of Sciences of the United States of America. 109(26):10546-51. PMID: 22689982.
- Thompson CC, Carabeo RA. (2011) An optimal method of iron starvation of the obligate intracellular pathogen, Chlamydia trachomatis. Front Microbiol. 2011 Feb 14;2:20. doi: 10.3389/fmicb.2011.00020. PMID: 21687412.
- Ouellette SP, Carabeo RA. (2010) A Functional Slow Recycling Pathway of Transferrin is Required for Growth of Chlamydia. Front Microbiol. 2010 Oct 8;1:112. doi: 10.3389/fmicb.2010.00112. PMID: 21607082.