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

Abstract

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. In this report, we identify a putative ortholog of Mre11 in P. falciparum (PfalMre11) that shares 22% sequence similarity to human Mre11. Homology modeling reveals striking structural resemblance of the predicted PfalMre11 nuclease domain to the nuclease domain of Saccharomyces cerevisiae Mre11 (ScMre11). Complementation analyses reveal functional conservation of PfalMre11 nuclease activity as demonstrated by the ability of the PfalMre11 nuclease domain, in conjunction with the C-terminal domain of ScMre11, to functionally complement an mre11 deficient yeast strain. Functional complementation was virtually abrogated by an amino acid substitution in the PfalMre11 nuclease domain (D398N). PfalMre11 is abundant in the mitotically active trophozoite and schizont stages of P. falciparum and is up-regulated in response to DNA damage, suggesting a role in the DDR. PfalMre11 exhibits physical interaction with PfalRad50. In addition, yeast 2-hybrid studies show that PfalMre11 interacts with ScRad50 and ScXrs2, two important components of the well characterized Mre11-Rad50-Xrs2 complex which is involved in DDR signaling and repair in S. cerevisiae, further supporting a role for PfalMre11 in the DDR. Taken together, these findings provide evidence that PfalMre11 is an evolutionarily conserved component of the DDR in Plasmodium.

Zinc finger nuclease-based double-strand breaks attenuate malaria parasites and reveal rare microhomology-mediated end joining

“…MMEJ has been shown to require six key proteins in mammals: MRE11, NBS1, LIGASE III, XRCC1, FEN1 and PARP1 [ 51 ]. Of these, only MRE11, XRCC1 and FEN1 have been identified in Plasmodium , and MRE11 has recently been characterised in P. falciparum [ 52 ]. Of those missing, DNA ligase III seems to be replaceable by DNA ligase I [ 53 ] and PARP1 is only present in the related parasite T. gondii , supporting its suggested role to compete with Ku for choice of repair pathway [ 54 ].…”

Chromosome End Repair and Genome Stability in Plasmodium falciparum

“…Therefore, how malaria parasites respond to DSBs and efficiently maintain genome integrity is unclear. Characterization of important enzymes involved in HR demonstrated that this pathway is functionally conserved ( 17 – 19 ). The subtelomeric regions, given their size, extensive gene content, semirepetitive nature, and unique chromatin structure, represent a particularly interesting region of the genome for studying DSB repair.…”

Homologous Recombination in Protozoan Parasites and Recombinase Inhibitors

“…BLM (Bloom syndrome protein) is a DNA helicase involved in DSB end-resection, and Pf Blm possessed helicase activity ( Rahman et al, 2016 ). The protein complex Mre11 (meiotic recombination 11), Rad50 (radiation-sensitive 50), and NBS1 (involved in Nijmegen breakage syndrome) recognizes and end-resects DNA DSBs, and Pf Mre11 demonstrated nuclease activity and interacted with Pf Rad50 ( Badugu et al, 2015 ). Lastly, diploid zygotes of Plasmodium undergo meiosis in the insect vector to produce haploid cells, a state in which Dmc1 becomes relevant.…”