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Phan IQ, Rice CA, Craig J, Noorai RE, McDonald JR, Subramanian S, Tillery L, Barrett LK, Shankar V, Morris JC, Van Voorhis WC, Kyle DE, Myler PJ. The transcriptome of Balamuthia mandrillaris trophozoites for structure-guided drug design. Sci Rep 2021; 11:21664. [PMID: 34737367 PMCID: PMC8569187 DOI: 10.1038/s41598-021-99903-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Accepted: 09/27/2021] [Indexed: 11/09/2022] Open
Abstract
Balamuthia mandrillaris, a pathogenic free-living amoeba, causes cutaneous skin lesions as well as granulomatous amoebic encephalitis, a 'brain-eating' disease. As with the other known pathogenic free-living amoebas (Naegleria fowleri and Acanthamoeba species), drug discovery efforts to combat Balamuthia infections of the central nervous system are sparse; few targets have been validated or characterized at the molecular level, and little is known about the biochemical pathways necessary for parasite survival. Current treatments of encephalitis due to B. mandrillaris lack efficacy, leading to case fatality rates above 90%. Using our recently published methodology to discover potential drugs against pathogenic amoebas, we screened a collection of 85 compounds with known antiparasitic activity and identified 59 compounds that impacted the growth of Balamuthia trophozoites at concentrations below 220 µM. Since there is no fully annotated genome or proteome of B. mandrillaris, we sequenced and assembled its transcriptome from a high-throughput RNA-sequencing (RNA-Seq) experiment and located the coding sequences of the genes potentially targeted by the growth inhibitors from our compound screens. We determined the sequence of 17 of these target genes and obtained expression clones for 15 that we validated by direct sequencing. These will be used in the future in combination with the identified hits in structure guided drug discovery campaigns to develop new approaches for the treatment of Balamuthia infections.
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Affiliation(s)
- Isabelle Q Phan
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA.
- Center for Global Infectious Disease Research, Seattle Children's Research Institute, Seattle, WA, USA.
| | - Christopher A Rice
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, USA.
- Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA, USA.
| | - Justin Craig
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA
| | - Rooksana E Noorai
- Clemson University Genomics and Bioinformatics Facility, Clemson University, Clemson, SC, USA
| | - Jacquelyn R McDonald
- Center for Global Infectious Disease Research, Seattle Children's Research Institute, Seattle, WA, USA
| | - Sandhya Subramanian
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA
- Center for Global Infectious Disease Research, Seattle Children's Research Institute, Seattle, WA, USA
| | - Logan Tillery
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA
| | - Lynn K Barrett
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA
| | - Vijay Shankar
- Center for Human Genetics, Clemson University, Greenwood, SC, USA
| | - James C Morris
- Eukaryotic Pathogens Innovation Center, Department of Genetics and Biochemistry, Clemson University, Clemson, SC, USA
| | - Wesley C Van Voorhis
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA
- Department of Microbiology, University of Washington, Seattle, WA, USA
- Department of Global Health, University of Washington, Seattle, WA, USA
| | - Dennis E Kyle
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, USA
| | - Peter J Myler
- Seattle Structural Genomics Center for Infectious Disease (SSGCID), Seattle, WA, USA.
- Center for Global Infectious Disease Research, Seattle Children's Research Institute, Seattle, WA, USA.
- Department of Global Health, University of Washington, Seattle, WA, USA.
- Department of Pediatrics, University of Washington, Seattle, WA, USA.
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Abstract
Unlike most other eukaryotes, Leishmania and other trypanosomatid protozoa have largely eschewed transcriptional control of gene expression, relying instead on posttranscriptional regulation of mRNAs derived from polycistronic transcription units (PTUs). In these parasites, a novel modified nucleotide base (β-d-glucopyranosyloxymethyluracil) known as J plays a critical role in ensuring that transcription termination occurs only at the end of each PTU, rather than at the polyadenylation sites of individual genes. To further understand the biology of J-associated processes, we used tandem affinity purification (TAP) tagging and mass spectrometry to reveal proteins that interact with the glucosyltransferase performing the final step in J synthesis. These studies identified four proteins reminiscent of subunits in the PTW/PP1 complex that controls transcription termination in higher eukaryotes. Moreover, bioinformatic analyses identified the DNA-binding subunit of Leishmania PTW/PP1 as a novel J-binding protein (JBP3), which is also part of another complex containing proteins with domains suggestive of a role in chromatin modification/remodeling. Additionally, JBP3 associates (albeit transiently and/or indirectly) with the trypanosomatid equivalent of the PAF1 complex involved in the regulation of transcription in other eukaryotes. The downregulation of JBP3 expression levels in Leishmania resulted in a substantial increase in transcriptional readthrough at the 3′ end of most PTUs. We propose that JBP3 recruits one or more of these complexes to the J-containing regions at the end of PTUs, where they halt the progression of the RNA polymerase. This decoupling of transcription termination from the splicing of individual genes enables the parasites’ unique reliance on polycistronic transcription and posttranscriptional regulation of gene expression. IMPORTANCELeishmania parasites cause a variety of serious human diseases, with no effective vaccine and emerging resistance to current drug therapy. We have previously shown that a novel DNA base called J is critical for transcription termination at the ends of the polycistronic gene clusters that are a hallmark of Leishmania and related trypanosomatids. Here, we describe a new J-binding protein (JBP3) associated with three different protein complexes that are reminiscent of those involved in the control of transcription in other eukaryotes. However, the parasite complexes have been reprogrammed to regulate transcription and gene expression in trypanosomatids differently than in the mammalian hosts, providing new opportunities to develop novel chemotherapeutic treatments against these important pathogens.
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