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Fulltext Coordination of apicoplast transcription in a malaria parasite by internal and host cues

Kobayashi Y, Komatsuya K, Imamura S, Nozaki T, Watanabe YI, Sato S, et al.

Proc Natl Acad Sci U S A, 2023 Jul 11;120(28):e2214765120.
PMID: 37406097 DOI: 10.1073/pnas.2214765120

The malaria parasite Plasmodium falciparum has a nonphotosynthetic plastid called the apicoplast, which contains its own genome. Regulatory mechanisms for apicoplast gene expression remain poorly understood, despite this organelle being crucial for the parasite life cycle. Here, we identify a nuclear-encoded apicoplast RNA polymerase σ subunit (sigma factor) which, along with the α subunit, appears to mediate apicoplast transcript accumulation. This has a periodicity reminiscent of parasite circadian or developmental control. Expression of the apicoplast subunit gene, apSig, together with apicoplast transcripts, increased in the presence of the blood circadian signaling hormone melatonin. Our data suggest that the host circadian rhythm is integrated with intrinsic parasite cues to coordinate apicoplast genome transcription. This evolutionarily conserved regulatory system might be a future target for malaria treatment.

Matched MeSH terms: Plasmodium falciparum/metabolism
Assembly of ligands interaction models for glutathione-S-transferases from Plasmodium falciparum, human and mouse using enzyme kinetics and molecular docking

Al-Qattan MN, Mordi MN, Mansor SM

Comput Biol Chem, 2016 10;64:237-249.
PMID: 27475235 DOI: 10.1016/j.compbiolchem.2016.07.007

BACKGROUND: Glutathione-s-transferases (GSTs) are enzymes that principally catalyze the conjugation of electrophilic compounds to the endogenous nucleophilic glutathione substrate, besides, they have other non-catalytic functions. The Plasmodium falciparum genome encodes a single isoform of GST (PfGST) which is involved in buffering the toxic heme, thus considered a potential anti-malarial target. In mammals several classes of GSTs are available, each of various isoforms. The human (human GST Pi-1 or hGSTP1) and mouse (murine GST Mu-1 or mGSTM1) GST isoforms control cellular apoptosis by interaction with signaling proteins, thus considered as potential anti-cancer targets. In the course of GSTs inhibitors development, the models of ligands interactions with GSTs are used to guide rational molecular modification. In the absence of X-ray crystallographic data, enzyme kinetics and molecular docking experiments can aid in addressing ligands binding modes to the enzymes.
METHODS: Kinetic studies were used to investigate the interactions between the three GSTs and each of glutathione, 1-chloro-2,4-dinitrobenzene, cibacron blue, ethacrynic acid, S-hexyl glutathione, hemin and protoporphyrin IX. Since hemin displacement is intended for PfGST inhibitors, the interactions between hemin and other ligands at PfGST binding sites were studied kinetically. Computationally determined binding modes and energies were interlinked with the kinetic results to resolve enzymes-ligands interaction models at atomic level.
RESULTS: The results showed that hemin and cibacron blue have different binding modes in the three GSTs. Hemin has two binding sites (A and B) with two binding modes at site-A depending on presence of GSH. None of the ligands were able to compete hemin binding to PfGST except ethacrynic acid. Besides bind differently in GSTs, the isolated anthraquinone moiety of cibacron blue is not maintaining sufficient interactions with GSTs to be used as a lead. Similarly, the ethacrynic acid uses water bridges to mediate interactions with GSTs and at least the conjugated form of EA is the true hemin inhibitor, thus EA may not be a suitable lead.
CONCLUSIONS: Glutathione analogues with bulky substitution at thiol of cysteine moiety or at γ-amino group of γ-glutamine moiety may be the most suitable to provide GST inhibitors with hemin competition.

Matched MeSH terms: Plasmodium falciparum/metabolism
Fulltext Tracking origins and spread of sulfadoxine-resistant Plasmodium falciparum dhps alleles in Thailand

Alam MT, Vinayak S, Congpuong K, Wongsrichanalai C, Satimai W, Slutsker L, et al.

Antimicrob Agents Chemother, 2011 Jan;55(1):155-64.
PMID: 20956597 DOI: 10.1128/AAC.00691-10

The emergence and spread of drug-resistant Plasmodium falciparum have been a major impediment for the control of malaria worldwide. Earlier studies have shown that similar to chloroquine (CQ) resistance, high levels of pyrimethamine resistance in P. falciparum originated independently 4 to 5 times globally, including one origin at the Thailand-Cambodia border. In this study we describe the origins and spread of sulfadoxine-resistance-conferring dihydropteroate synthase (dhps) alleles in Thailand. The dhps mutations and flanking microsatellite loci were genotyped for P. falciparum isolates collected from 11 Thai provinces along the Burma, Cambodia, and Malaysia borders. Results indicated that resistant dhps alleles were fixed in Thailand, predominantly being the SGEGA, AGEAA, and SGNGA triple mutants and the AGKAA double mutant (mutated codons are underlined). These alleles had different geographical distributions. The SGEGA alleles were found mostly at the Burma border, while the SGNGA alleles occurred mainly at the Cambodia border and nearby provinces. Microsatellite data suggested that there were two major genetic lineages of the triple mutants in Thailand, one common for SGEGA/SGNGA alleles and another one independent for AGEAA. Importantly, the newly reported SGNGA alleles possibly originated at the Thailand-Cambodia border. All parasites in the Yala province (Malaysia border) had AGKAA alleles with almost identical flanking microsatellites haplotypes. They were also identical at putatively neutral loci on chromosomes 2 and 3, suggesting a clonal nature of the parasite population in Yala. In summary, this study suggests multiple and independent origins of resistant dhps alleles in Thailand.

Matched MeSH terms: Plasmodium falciparum/metabolism*
Fulltext Plasmodium falciparum 19 kDa of merozoite surface protein-1 (MSP-1(19)) expressed in Mycobacterium bovis bacille Calmette Guerin (BCG) is reactive with an inhibitory but not a blocking monoclonal antibody

Nurul AA, Rapeah S, Norazmi MN

Trop Biomed, 2010 Apr;27(1):60-7.
PMID: 20562815

Proteins on the surface of Plasmodium falciparum merozoites are good targets for vaccine development against malaria because they are accessible to antibodies in the plasma. The 19 kDa C-terminus of merozoite surface protein-1 (MSP-1(19)) has been shown to induce both inhibitory as well as blocking antibodies, the latter blocking the protective effects of the former. Inhibitory antibodies bind to MSP-1(19) and inhibit merozoite invasion of red blood cells (RBC) but the binding of blocking antibodies can prevent binding of inhibitory antibodies thereby allowing the parasite to invade RBC. We constructed a synthetic version of the MSP-1(19) of the P. falciparum using mycobacterium codon usage by assembly PCR. The synthetic MSP-1(19) was mutated at various sites to promote the production of inhibitory but not blocking antibodies as previously reported. The native and mutated MSP-1(19) were cloned and expressed in Mycobacterium bovis bacille Calmette-Guerin (BCG) and the expressions of the recombinant proteins were detected by specific monoclonal antibodies (mAbs) namely, 12.10 and 1E1 against MSP-1(19) using Western blotting. The mutated MSP-1(19) protein reacted with the inhibitory mAb, 12.10, but not the blocking mAb, 1E1, paving the way for the construction of a potential recombinant BCG (rBCG) blood stage vaccine against malaria.

Matched MeSH terms: Plasmodium falciparum/metabolism*
Fulltext The Plasmodium falciparum male gametocyte protein P230p, a paralog of P230, is vital for ookinete formation and mosquito transmission

Marin-Mogollon C, van de Vegte-Bolmer M, van Gemert GJ, van Pul FJA, Ramesar J, Othman AS, et al.

Sci Rep, 2018 10 08;8(1):14902.
PMID: 30297725 DOI: 10.1038/s41598-018-33236-x

Two members of 6-cysteine (6-cys) protein family, P48/45 and P230, are important for gamete fertility in rodent and human malaria parasites and are leading transmission blocking vaccine antigens. Rodent and human parasites encode a paralog of P230, called P230p. While P230 is expressed in male and female parasites, P230p is expressed only in male gametocytes and gametes. In rodent malaria parasites this protein is dispensable throughout the complete life-cycle; however, its function in P. falciparum is unknown. Using CRISPR/Cas9 methodology we disrupted the gene encoding Pfp230p resulting in P. falciparum mutants (PfΔp230p) lacking P230p expression. The PfΔp230p mutants produced normal numbers of male and female gametocytes, which retained expression of P48/45 and P230. Upon activation male PfΔp230p gametocytes undergo exflagellation and form male gametes. However, male gametes are unable to attach to red blood cells resulting in the absence of characteristic exflagellation centres in vitro. In the absence of P230p, zygote formation as well as oocyst and sporozoite development were strongly reduced (>98%) in mosquitoes. These observations demonstrate that P230p, like P230 and P48/45, has a vital role in P. falciparum male fertility and zygote formation and warrants further investigation as a potential transmission blocking vaccine candidate.

Matched MeSH terms: Plasmodium falciparum/metabolism*
Diversity and natural selection of Merozoite surface Protein-1 in three species of human malaria parasites: Contribution from South-East Asian isolates

Goh XT, Lim YAL, Lee PC, Nissapatorn V, Chua KH

Mol Biochem Parasitol, 2021 07;244:111390.
PMID: 34087264 DOI: 10.1016/j.molbiopara.2021.111390

The present study aimed to examine the genetic diversity of human malaria parasites (i.e., P. falciparum, P. vivax and P. knowlesi) in Malaysia and southern Thailand targeting the 19-kDa C-terminal region of Merozoite Surface Protein-1 (MSP-119). This region is essential for the recognition and invasion of erythrocytes and it is considered one of the leading candidates for asexual blood stage vaccines. However, the genetic data of MSP-119 among human malaria parasites in Malaysia is limited and there is also a need to update the current sequence diversity of this gene region among the Thailand isolates. In this study, genomic DNA was extracted from 384 microscopy-positive blood samples collected from patients who attended the hospitals or clinics in Malaysia and malaria clinics in Thailand from the year 2008 to 2016. The MSP-119 was amplified using PCR followed by bidirectional sequencing. DNA sequences identified in the present study were subjected to Median-joining network analysis with sequences of MSP-119 obtained from GenBank. DNA sequence analysis revealed that PfMSP-119 of Malaysian and Thailand isolates was not genetically conserved as high number of haplotypes were detected and positive selection was prevalent in PfMSP-119, hence questioning its suitability to be used as a vaccine candidate. A novel haplotype (Q/TNG/L) was also detected in Thailand P. falciparum isolate. In contrast, PvMSP-119 was highly conserved, however for the first time, a non-synonymous substitution (A1657S) was reported among Malaysian isolates. As for PkMSP-119, the presence of purifying selection and low nucleotide diversity indicated that it might be a potential vaccine target for P. knowlesi.

Matched MeSH terms: Plasmodium falciparum/metabolism
Fulltext Heterologous Expression of a Novel Drug Transporter from the Malaria Parasite Alters Resistance to Quinoline Antimalarials

Tindall SM, Vallières C, Lakhani DH, Islahudin F, Ting KN, Avery SV

Sci Rep, 2018 02 06;8(1):2464.
PMID: 29410428 DOI: 10.1038/s41598-018-20816-0

Antimalarial drug resistance hampers effective malaria treatment. Critical SNPs in a particular, putative amino acid transporter were recently linked to chloroquine (CQ) resistance in malaria parasites. Here, we show that this conserved protein (PF3D7_0629500 in Plasmodium falciparum; AAT1 in P. chabaudi) is a structural homologue of the yeast amino acid transporter Tat2p, which is known to mediate quinine uptake and toxicity. Heterologous expression of PF3D7_0629500 in yeast produced CQ hypersensitivity, coincident with increased CQ uptake. PF3D7_0629500-expressing cultures were also sensitized to related antimalarials; amodiaquine, mefloquine and particularly quinine. Drug sensitivity was reversed by introducing a SNP linked to CQ resistance in the parasite. Like Tat2p, PF3D7_0629500-dependent quinine hypersensitivity was suppressible with tryptophan, consistent with a common transport mechanism. A four-fold increase in quinine uptake by PF3D7_0629500 expressing cells was abolished by the resistance SNP. The parasite protein localised primarily to the yeast plasma membrane. Its expression varied between cells and this heterogeneity was used to show that high-expressing cell subpopulations were the most drug sensitive. The results reveal that the PF3D7_0629500 protein can determine the level of sensitivity to several major quinine-related antimalarials through an amino acid-inhibitable drug transport function. The potential clinical relevance is discussed.

Matched MeSH terms: Plasmodium falciparum/metabolism