Plasmodium falciparum GBP2 Is a Telomere-Associated Protein That Binds to G-Quadruplex DNA and RNA

Abstract

In the early-diverging protozoan parasite Plasmodium, few telomere-binding proteins have been identified and several are unique. Plasmodium telomeres, like those of most eukaryotes, contain guanine-rich repeats that can form G-quadruplex structures. In model systems, quadruplex-binding drugs can disrupt telomere maintenance and some quadruplex-binding drugs are potent anti-plasmodial agents. Therefore, telomere-interacting and quadruplex-interacting proteins may offer new targets for anti-malarial therapy. Here, we report that P. falciparum GBP2 is such a protein. It was identified via ‘Proteomics of Isolated Chromatin fragments’, applied here for the first time in Plasmodium. In vitro, PfGBP2 binds specifically to G-rich telomere repeats in quadruplex form and it can also bind to G-rich RNA. In vivo, PfGBP2 partially colocalises with the known telomeric protein HP1 but is also found in the cytoplasm, probably due to its affinity for RNA. Consistently, its interactome includes numerous RNA-associated proteins. PfGBP2 is evidently a multifunctional DNA/RNA-binding factor in Plasmodium.

Nonsense-mediated decay machinery in Plasmodium falciparum is inefficient and non-essential

“…5A , dotted line) ( 42 ). This suggests that interactions between UPF2, ALBA4, and GBP2 are conserved in Plasmodium ( 42 ), and in P. falciparum Pf GBP2 binds to RNA as well as to DNA ( 43 ). In yeast, Gbp2 is an SR (serine-arginine) protein that marks unspliced transcripts and targets them for elimination via the nuclear exosome ( 44 ).…”

Effects of the G-quadruplex-binding drugs quarfloxin and CX-5461 on the malaria parasite Plasmodium falciparum

“…ThT G4 binding assays were performed as described previously ( Edwards-Smallbone et al, 2022 ). To allow for G4 folding, 40 μM synthetic DNA oligonucleotides (Sigma Aldrich) with 100 μM Tris buffer (pH 7.8) and 100 μM KCl were heated to 90 °C for 5 min, before cooling to room temperature at a rate of 1 °C/min.…”

“…Being a nucleic acid structure rather than a protein, the G4 would represent an entirely novel drug target in the parasite. P. falciparum has a highly A/T-biased genome (∼81% A/T) ( Gardner et al, 2002 ) with very few sequences that have the potential to form G4s (‘PQSs’); nevertheless, we and others have shown that these G4s do exist and that they play roles in Plasmodium biology at both the DNA ( Gage and Merrick, 2020 ; Gazanion et al, 2020 ; Harris et al, 2018 ; Smargiasso et al, 2009 ) and RNA ( Dumetz et al, 2021 ; Edwards-Smallbone et al, 2022 ) levels. The existence of G4s in malaria parasites raises the possibility of repositioning G4-binding compounds – which are often developed primarily as anticancer agents – as antimalarial agents.…”

Telomeres and Telomerase as Promising Targets for Malaria Therapy: A Comprehensive Review

“…Additionally, disease severity depends on parasite load in the host species [77,78]. In P. falciparum, the telomere-associated sequence (TAS), which is 15-30 kb in length, precedes each of the 14 linear chromosomes of the parasite [79,80].…”