DNA topoisomerase II is involved in regulation of cyst wall protein genes and differentiation in Giardia lamblia

Type II DNA Topoisomerases in trypanosomatid and apicomplexan parasites

Diseases caused by trypanosomatid parasites have no commercially available vaccines for human application. Treatment modalities completely rely on chemotherapeutics strategies that often exhibit clinical drawbacks, like host toxicity, side effects and treatment failure for drug resistance. These, in many instances, are costly, making them unaffordable for certain groups of beneficiaries. To find reasonable solutions, researchers are attempting to identify and validate new drug targets that would offer parasite specificity. DNA topoisomerases in parasites present a consolidated class of drug targets due to their multiple structural and functional differences with host homologs. Type II DNA topoisomerases in these parasites, in particular, have been attracting interest of scientific community attributable to their pivotal role in the replication of the atypical DNA. In this article, we present a detailed review of structural and functional features of type II DNA topoisomerases of clinically-relevant trypanosomatid and apicomplexan parasites. Also, we provide up-to-date information on different molecules that target these enzymes. Altogether, the review will largely help in understanding the rationale for exploiting type II DNA topoisomerases in these groups of parasites as drug targets.

DNA Topoisomerases in the Unicellular Protozoan Parasites: Unwinding the Mystery

DNA topoisomerases are a group of enzymes present ubiquitously in all organisms from unicellular protozoan parasites to humans. These enzymes control the topological problems caused by DNA double helix in the cell during nucleic acid metabolism. Certain types of topoisomerases present in unicellular parasites are quite different from human topoisomerases (hTop) concerning structure, expression, and function. Many protozoan parasites causing fatal diseases have DNA topoisomerases, which play vital roles in their survival. Given the fact that the structures of the protozoan parasite topoisomerases are different from humans, DNA topoisomerase acts as an essential target for potent drug development for parasitic diseases. Moreover, various studies revealed the therapeutic potential of these drugs targeting the parasitic topoisomerases. Therefore, the characterization of parasitic topoisomerases is pivotal for the development of future potential drug targets. Considering the importance of this ubiquitous enzyme as a potential drug target, we describe in detail all the reported protozoan topoisomerases in an organized manner including Leishmania, Trypanosoma, Plasmodium, Giardia, Entamoeba, Babesia, Theileria, Crithidia, Cryptosporidium, Toxoplasma, etc. This review highlights the unique attributes associated with the structure and function of different types of DNA topoisomerases from the unicellular protozoan parasites. So, it would be beneficial for researchers to obtain awareness about the currently characterized topoisomerases and the ones that need better characterization, understand the structure-function relationship of parasitic topoisomerases, to develop the potent anti-parasitic drugs, and also provides a future platform for therapeutic development.

A Novel Spo11 Homologue Functions as a Positive Regulator in Cyst Differentiation in Giardia lamblia

Giardia lamblia persists in a dormant state with a protective cyst wall for transmission. It is incompletely known how three cyst wall proteins (CWPs) are coordinately synthesized during encystation. Meiotic recombination is required for sexual reproduction in animals, fungi, and plants. It is initiated by formation of double-stranded breaks by a topoisomerase-like Spo11. It has been shown that exchange of genetic material in the fused nuclei occurs during Giardia encystation, suggesting parasexual recombination processes of this protozoan. Giardia possesses an evolutionarily conserved Spo11 with typical domains for cleavage reaction and an upregulated expression pattern during encystation. In this study, we asked whether Spo11 can activate encystation process, like other topoisomerases we previously characterized. We found that Spo11 was capable of binding to both single-stranded and double-stranded DNA in vitro and that it could also bind to the cwp promoters in vivo as accessed in chromatin immunoprecipitation assays. Spo11 interacted with WRKY and MYB2 (named from myeloblastosis), transcription factors that can activate cwp gene expression during encystation. Interestingly, overexpression of Spo11 resulted in increased expression of cwp1-3 and myb2 genes and cyst formation. Mutation of the Tyr residue for the active site or two conserved residues corresponding to key DNA-binding residues for Arabidopsis Spo11 reduced the levels of cwp1-3 and myb2 gene expression and cyst formation. Targeted disruption of spo11 gene with CRISPR/Cas9 system led to a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that Spo11 acts as a positive regulator for Giardia differentiation into cyst.

ATP-Diphosphohydrolases in Parasites: Localization, Functions and Recent Developments in Drug Discovery

ATP-diphosphohydrolases (EC 3.6.1.5), also known as ATPDases, NTPases, NTPDases, EATPases or apyrases, are enzymes that hydrolyze a variety of nucleoside tri- and diphosphates to their respective nucleosides, being their activities dependent on the presence of divalent cations, such as calcium and magnesium. Recently, ATP-diphosphohydrolases were identified on the surface of several parasites, such as Trypanosoma sp, Leishmania sp and Schistosoma sp. In parasites, the activity of ATPdiphosphohydrolases has been associated with the purine recuperation and/or as a protective mechanism against the host organism under conditions that involve ATP or ADP, such as immune responses and platelet activation. These proteins have been suggested as possible targets for the development of new antiparasitic drugs. In this review, we will comprehensively address the main aspects of the location and function of ATP-diphosphohydrolase in parasites. Also, we performed a detailed research in scientific database of recent developments in new natural and synthetic inhibitors of the ATPdiphosphohydrolases in parasites.

DNA topoisomerase IIIβ promotes cyst generation by inducing cyst wall protein gene expression in Giardia lamblia

Giardia lamblia causes waterborne diarrhoea by transmission of infective cysts. Three cyst wall proteins are highly expressed in a concerted manner during encystation of trophozoites into cysts. However, their gene regulatory mechanism is still largely unknown. DNA topoisomerases control topological homeostasis of genomic DNA during replication, transcription and chromosome segregation. They are involved in a variety of cellular processes including cell cycle, cell proliferation and differentiation, so they may be valuable drug targets. Giardia lamblia possesses a type IA DNA topoisomerase (TOP3β) with similarity to the mammalian topoisomerase IIIβ. We found that TOP3β was upregulated during encystation and it possessed DNA-binding and cleavage activity. TOP3β can bind to the cwp promoters in vivo using norfloxacin-mediated topoisomerase immunoprecipitation assays. We also found TOP3β can interact with MYB2, a transcription factor involved in the coordinate expression of cwp1-3 genes during encystation. Interestingly, overexpression of TOP3β increased expression of cwp1-3 and myb2 genes and cyst formation. Microarray analysis confirmed upregulation of cwp1-3 and myb2 genes by TOP3β. Mutation of the catalytically important Tyr residue, deletion of C-terminal zinc ribbon domain or further deletion of partial catalytic core domain reduced the levels of cleavage activity, cwp1-3 and myb2 gene expression, and cyst formation. Interestingly, some of these mutant proteins were mis-localized to cytoplasm. Using a CRISPR/Cas9 system for targeted disruption of top3β gene, we found a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that TOP3β may be functionally conserved, and involved in inducing Giardia cyst formation.

Development of CRISPR/Cas9-mediated gene disruption systems in Giardia lamblia

Giardia lamblia becomes dormant by differentiation into a water-resistant cyst that can infect a new host. Synthesis of three cyst wall proteins (CWPs) is the fundamental feature of this differentiation. Myeloid leukemia factor (MLF) proteins are involved in cell differentiation, and tumorigenesis in mammals, but little is known about its role in protozoan parasites. We developed a CRISPR/Cas9 system to understand the role of MLF in Giardia. Due to the tetraploid genome in two nuclei of Giardia, it could be hard to disrupt a gene completely in Giardia. We only generated knockdown but not knockout mutants. We found that knockdown of the mlf gene resulted in a significant decrease of cwp gene expression and cyst formation, suggesting a positive role of MLF in encystation. We further used mlf as a model gene to improve the system. The addition of an inhibitor for NHEJ, Scr7, or combining all cassettes for gRNA and Cas9 expression into one plasmid resulted in improved gene disruption efficiencies and a significant decrease in cwp gene expression. Our results provide insights into a positive role of MLF in inducing Giardia differentiation and a useful tool for studies in Giardia.

DNA Topoisomerases in Unicellular Pathogens: Structure, Function, and Druggability

All organisms, including unicellular pathogens, compulsorily possess DNA topoisomerases for successful nucleic acid metabolism. But particular subtypes of topoisomerases exist, in all prokaryotes and in some unicellular eukaryotes, that are absent in higher eukaryotes. Moreover, topoisomerases from pathogenic members of a niche possess some unique molecular architecture and functionalities completely distinct from their nonpathogenic colleagues. This review will highlight the unique attributes associated with the structures and functions of topoisomerases from the unicellular pathogens, with special reference to bacteria and protozoan parasites. It will also summarise the progress made in the domain pertaining to the druggability of these topoisomerases, upon which a future platform for therapeutic development can be successfully constructed.