Identification of a chaperone-code responsible for Rad51-mediated genome repair.

Posttranslational modifications of Hsp90 are known to regulate its in vivo chaperone functions. Here, we demonstrate that the lysine acetylation-deacetylation dynamics of Hsp82 is a major determinant in DNA repair mediated by Rad51. We uncover that the deacetylated lysine 27 in Hsp82 dictates the formation of the Hsp82-Aha1-Rad51 complex, which is crucial for client maturation.

Correction: Identification of Plasmodium falciparum DNA Repair Protein Mre11 with an Evolutionarily Conserved Nuclease Function.

[This corrects the article DOI: 10.1371/journal.pone.

Topoisomerase VIB and Spo11 Constitute Functional Type IIB Topoisomerase in Malaria Parasite: Its Possible Role in Mitochondrial DNA Segregation.

The human malaria parasite undergoes a noncanonical cell division, namely, endoreduplication, where several rounds of nuclear, mitochondrial, and apicoplast replication occur without cytoplasmic division. Despite its importance in biology, the topoisomerases essential for decatenation of replicated chromosome during endoreduplication remain elusive. We hypothesize that the topoisomerase VI complex, containing Plasmodium falciparum topiosomerase VIB (PfTopoVIB) and catalytic P.

DNA damage-induced nuclear import of HSP90α is promoted by Aha1.

The interplay between yHSP90α (Hsp82) and Rad51 has been implicated in the DNA double-strand break repair (DSB) pathway in yeast. Here we report that nuclear translocation of yHSP90α and its recruitment to the DSB end are essential for homologous recombination (HR)-mediated DNA repair in yeast. The HsHSP90α possesses an amino-terminal extension which is phosphorylated upon DNA damage.

A tale of topoisomerases and the knotty genetic material in the backdrop of Plasmodium biology.

The untangling or overwinding of genetic material is an inevitable part of DNA replication, repair, recombination, and transcription. Topoisomerases belong to a conserved enzyme family that amends DNA topology during various processes of DNA metabolism. To relax the genetic material, topoisomerases transiently break the phosphodiester bond on one or both DNA strands and remain associated with the cleavage site by forming a covalent enzyme-DNA intermediate.

Bloom Helicase Along with Recombinase Rad51 Repairs the Mitochondrial Genome of the Malaria Parasite.

The homologous recombination (HR) pathway has been implicated as the predominant mechanism for the repair of chromosomal DNA double-strand breaks (DSBs) of the malarial parasite. Although the extrachromosomal mitochondrial genome of this parasite experiences a greater number of DSBs due to its close proximity to the electron transport chain, nothing is known about the proteins involved in the repair of the mitochondrial genome. We investigated the involvement of nucleus-encoded HR proteins in the repair of the mitochondrial genome, as this genome does not code for any DNA repair proteins.

Synergistic Action between PfHsp90 Inhibitor and PfRad51 Inhibitor Induces Elevated DNA Damage Sensitivity in the Malaria Parasite.

The DNA recombinase Rad51 from the human malaria parasite Plasmodium falciparum has emerged as a potential drug target due to its central role in the homologous recombination (HR)-mediated double-strand break (DSB) repair pathway. Inhibition of the ATPase and strand exchange activity of Rad51 (PfRad51) by a small-molecule inhibitor, B02 [3-(phenylmethyl)-2-[(1E)-2-(3-pyridinyl)ethenyl]-4(3H)-quinazolinone], renders the parasite more sensitive to genotoxic agents. Here, we investigated whether the inhibition of the molecular chaperone PfHsp90 potentiates the antimalarial action of B02.

Molecular docking and molecular dynamics simulation identify a novel Radicicol derivative that predicts exclusive binding to Topoisomerase VIB.

harbors a unique type II topoisomerase, Topoisomerase VIB (TopoVIB), expressed specifically at the actively replicating stage of the parasite. An earlier study showed that Radicicol inhibits the decatenation activity of TopoVIB and thereby arrests the parasites at the schizont stage. Radicicol targets a unique ATP-binding fold called the Bergerat fold, which is also present in the N-terminal domain of the heat shock protein 90 (Hsp90).

Febrile temperature causes transcriptional downregulation of Plasmodium falciparum Sirtuins through Hsp90-dependent epigenetic modification.

Sirtuins (PfSIR2A and PfSIR2B) are implicated to play pivotal roles in the silencing of sub-telomeric genes and the maintenance of telomere length in P. falciparum 3D7 strain. Here, we identify the key factors that regulate the cellular abundance and activity of these two histone deacetylases.

Elucidation of DNA Repair Function of PfBlm and Potentiation of Artemisinin Action by a Small-Molecule Inhibitor of RecQ Helicase.

Artemisinin (ART)-based combination therapies are recommended as first- and second-line treatments for malaria. Here, we investigated the impact of the RecQ inhibitor ML216 on the repair of ART-mediated damage in the genome of and were identified as members of the RecQ helicase family in However, the role of these RecQ helicases in DNA double-strand break (DSB) repair in this parasite has not been explored. Here, we provide several lines of evidence to establish the involvement of PfBlm in DSB repair in First, we demonstrate that PfBlm interacts with two well-characterized DSB repair proteins of this parasite, namely, PfRad51 and PfalMre11.

A small-molecule inhibitor of the DNA recombinase Rad51 from synergizes with the antimalarial drugs artemisinin and chloroquine.

Malaria parasites repair DNA double-strand breaks (DSBs) primarily through homologous recombination (HR). Here, because the unrepaired DSBs lead to the death of the unicellular parasite , we investigated its recombinase, PfRad51, as a potential drug target. Undertaking an screening approach, we identified a compound, B02, that docks to the predicted tertiary structure of PfRad51 with high affinity.

Glu-108 in Saccharomyces cerevisiae Rad51 Is Critical for DNA Damage-Induced Nuclear Function.

DNA damage-induced Rad51 focus formation is the hallmark of homologous recombination-mediated DNA repair. Earlier, we reported that Rad51 physically interacts with Hsp90, and under the condition of Hsp90 inhibition, it undergoes proteasomal degradation. Here, we show that the dynamic interaction between Rad51 and Hsp90 is crucial for the DNA damage-induced nuclear function of Rad51.

Hsp90 Is Essential for Chl1-Mediated Chromosome Segregation and Sister Chromatid Cohesion.

Recent studies have demonstrated that aberrant sister chromatid cohesion causes genomic instability and hence is responsible for the development of a tumor. The Chl1 (chromosome loss 1) protein (homolog of human ChlRl/DDX11 helicase) plays an essential role in the proper segregation of chromosomes during mitosis. The helicase activity of Chl1 is critical for sister chromatid cohesion.

Plasmodium Hsp40 and human Hsp70: A potential cochaperone-chaperone complex.

Out of the total forty four members of Plasmodium falciparum Hsp40 protein family, nineteen of them possess a PEXEL motif, and are predicted to be exported into the cytosol of an infected RBC. It is speculated that the human Hsp70 (hHsp70), which resides into the cytosol of the host erythrocyte, along with the exported PfHsp40s assists in the folding of parasitic proteins, thus playing a crucial role in the establishment of virulence. However, till date no experimental evidence supports this hypothesis.

Hsp90 induces increased genomic instability toward DNA-damaging agents by tuning down RAD53 transcription.

It is well documented that elevated body temperature causes tumors to regress upon radiotherapy. However, how hyperthermia induces DNA damage sensitivity is not clear. We show that a transient heat shock and particularly the concomitant induction of Hsp90 lead to increased genomic instability under DNA-damaging conditions.

Radicicol-Mediated Inhibition of Topoisomerase VIB-VIA Activity of the Human Malaria Parasite Plasmodium falciparum.

Plasmodium falciparum topoisomerase VIB (TopoVIB)-TopoVIA (TopoVIB-VIA) complex can be potentially exploited as a drug target against malaria due to its absence from the human genome. Previous work in our laboratory has suggested that P. falciparum TopoVIB (PfTopoVIB) might be a target of radicicol since treatment of parasite cultures with this antibiotic is associated with upregulation of Plasmodium TopoVIB at the transcript level as well as at the protein level.

Hsp90, the concertmaster: tuning transcription.

In the last decade, Hsp90 has emerged as a major regulator of cancer cell growth and proliferation. In cancer cells, it assists in giving maturation to oncogenic proteins including several kinases and transcription factors (TF). Recent studies have shown that apart from its chaperone activity, it also imparts regulation of transcription machinery and thereby alters the cellular physiology.

Identification of Plasmodium falciparum DNA Repair Protein Mre11 with an Evolutionarily Conserved Nuclease Function.

The eukaryotic Meiotic Recombination protein 11 (Mre11) plays pivotal roles in the DNA damage response (DDR). Specifically, Mre11 senses and signals DNA double strand breaks (DSB) and facilitates their repair through effector proteins belonging to either homologous recombination (HR) or non-homologous end joining (NHEJ) repair mechanisms. In the human malaria parasite Plasmodium falciparum, HR and alternative-NHEJ have been identified; however, little is known about the upstream factors involved in the DDR of this organism.

Heat stress-induced Cup9-dependent transcriptional regulation of SIR2.

The epigenetic writer Sir2 maintains the heterochromatin state of chromosome in three chromosomal regions, namely, the silent mating type loci, telomeres, and the ribosomal DNA (rDNA). In this study, we demonstrated the mechanism by which Sir2 is regulated under heat stress. Our study reveals that a transient heat shock causes a drastic reduction in the SIR2 transcript which results in sustained failure to initiate silencing for as long as 90 generations.

Both the charged linker region and ATPase domain of Hsp90 are essential for Rad51-dependent DNA repair.

The inhibition of Hsp90 in cancerous cells has been correlated with the reduction in double-strand break (DSB repair) activity. However, the precise effect of Hsp90 on the DSB repair pathway in normal cells has remained enigmatic. Our results show that the Hsp82 chaperone, the ortholog of mammalian Hsp90, is indispensable for homologous-recombination (HR)-mediated DNA repair in the budding yeast Saccharomyces cerevisiae.

Dominant negative mutant of Plasmodium Rad51 causes reduced parasite burden in host by abrogating DNA double-strand break repair.

Malaria parasites survive through repairing a plethora of DNA double-stranded breaks (DSBs) experienced during their asexual growth. In Plasmodium Rad51 mediated homologous recombination (HR) mechanism and homology-independent alternative end-joining mechanism have been identified. Here we address whether loss of HR activity can be compensated by other DSB repair mechanisms.

Radicicol confers mid-schizont arrest by inhibiting mitochondrial replication in Plasmodium falciparum.

Radicicol, an antifungal antibiotic, was previously identified as a compound having antimalarial activity. However, its mechanism of action in Plasmodium falciparum was not elucidated. While characterizing its antimalarial function, we observed that radicicol manifested two distinct developmental defects in cultured P.

Plasmodium falciparum origin recognition complex subunit 1 (PfOrc1) functionally complements Δsir3 mutant of Saccharomyces cerevisiae.

Telomere position effect efficiently controls silencing of subtelomeric var genes, which are involved in antigenic variation in human malaria parasite Plasmodium falciparum. Although, PfOrc1 has been found to be associated with PfSir2 in the silencing complex, its function in telomere silencing remained uncertain especially due to an apparent lack of BAH domain at its amino-terminal region. Here we report that PfOrc1 possesses a Sir3/Orc1 like silencing activity.

Characterization of Rad51 from apicomplexan parasite Toxoplasma gondii: an implication for inefficient gene targeting.

Repairing double strand breaks (DSBs) is absolutely essential for the survival of obligate intracellular parasite Toxoplasma gondii. Thus, DSB repair mechanisms could be excellent targets for chemotherapeutic interventions. Recent genetic and bioinformatics analyses confirm the presence of both homologous recombination (HR) as well as non homologous end joining (NHEJ) proteins in this lower eukaryote.