RESUMO
Plasmodium falciparum erythrocyte invasion is a multistep process that involves a spectrum of interactions that are not well characterized. We have characterized a 113-kDa immunogenic protein, PF3D7_1431400 (PF14_0293), that possesses coiled-coil structures. The protein is localized on the surfaces of both merozoites and gametocytes, hence the name Plasmodium falciparum surface-related antigen (PfSRA). The processed 32-kDa fragment of PfSRA binds normal human erythrocytes with different sensitivities to enzyme treatments. Temporal imaging from initial attachment to internalization of viable merozoites revealed that a fragment of PfSRA, along with PfMSP119, is internalized after invasion. Moreover, parasite growth inhibition assays showed that PfSRA P1 antibodies potently inhibited erythrocyte invasion of both sialic acid-dependent and -independent parasite strains. Also, immunoepidemiological studies show that malaria-infected populations have naturally acquired antibodies against PfSRA. Overall, the results demonstrate that PfSRA has the structural and functional characteristics of a very promising target for vaccine development.
Assuntos
Anticorpos Antiprotozoários/sangue , Antígenos de Protozoários/imunologia , Malária Falciparum/prevenção & controle , Proteínas de Membrana/imunologia , Plasmodium falciparum/imunologia , Proteínas de Protozoários/imunologia , Antígenos de Protozoários/metabolismo , Criança , Pré-Escolar , Descoberta de Drogas/métodos , Endocitose , Humanos , Vacinas Antimaláricas/imunologia , Malária Falciparum/imunologia , Proteínas de Membrana/metabolismo , Ligação Proteica , Proteínas de Protozoários/metabolismoRESUMO
The apicoplast, a relict plastid found in most species of the phylum Apicomplexa, harbors the ferredoxin redox system which supplies electrons to enzymes of various metabolic pathways in this organelle. Recent reports in Toxoplasma gondii and Plasmodium falciparum have shown that the iron-sulfur cluster (FeS)-containing ferredoxin is essential in tachyzoite and blood-stage parasites, respectively. Here we review ferredoxin's crucial contribution to isoprenoid and lipoate biosynthesis as well as tRNA modification in the apicoplast, highlighting similarities and differences between the two species. We also discuss ferredoxin's potential role in the initial reductive steps required for FeS synthesis as well as recent evidence that offers an explanation for how NADPH required by the redox system might be generated in Plasmodium spp.
Assuntos
Apicomplexa , Apicoplastos , Toxoplasma , Apicomplexa/genética , Apicomplexa/metabolismo , Apicoplastos/genética , Elétrons , Ferredoxinas/genética , Ferredoxinas/metabolismo , Ferro/metabolismo , NADP/metabolismo , Oxirredução , Plasmodium falciparum/genética , Plasmodium falciparum/metabolismo , RNA de Transferência/metabolismo , Enxofre/metabolismo , Terpenos/metabolismo , Toxoplasma/genéticaRESUMO
IMPACT STATEMENT: Plasmodium falciparum malaria is a global health problem. Erythrocyte invasion by P. falciparum merozoites appears to be a promising target to curb malaria. We have identified and characterized a novel protein that is involved in erythrocyte invasion. Our data on protein subcellular localization, stage-specific protein expression pattern, and merozoite invasion inhibition by α-peptide antibodies suggest a role for PF3D7_1459400 protein during P. falciparum erythrocyte invasion. Even more, the human immunoepidemiology data present PF3D7_1459400 protein as an immunogenic antigen which could be further exploited for the development of new anti-infective therapy against malaria.
Assuntos
Eritrócitos/parasitologia , Plasmodium falciparum/metabolismo , Proteínas de Protozoários/metabolismo , Adulto , Sequência de Aminoácidos , Animais , Anticorpos Antiprotozoários/imunologia , Sequência Conservada , Humanos , Estágios do Ciclo de Vida , Plasmodium falciparum/crescimento & desenvolvimento , Plasmodium falciparum/imunologia , Proteínas de Protozoários/química , Ratos , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Frações Subcelulares/metabolismoRESUMO
Nearly half of the genes in the Plasmodium falciparum genome have not yet been functionally investigated. We used homology-based structural modeling to identify multiple copies of Armadillo repeats within one uncharacterized gene expressed during the intraerythrocytic stages, PF3D7_0410600, subsequently referred to as P. falciparum Armadillo-Type Repeat Protein (PfATRP). Soluble recombinant PfATRP was expressed in a bacterial expression system, purified to apparent homogeneity and the identity of the recombinant PfATRP was confirmed by mass spectrometry. Affinity-purified α-PfATRP rabbit antibodies specifically recognized the recombinant protein. Immunofluorescence assays revealed that α-PfATRP rabbit antibodies reacted with P. falciparum schizonts. Anti-PfATRP antibody exhibited peripheral staining patterns around the merozoites. Given the localization of PfATRP in merozoites, we tested for an egress phenotype during schizont arrest assays and demonstrated that native PfATRP is inaccessible on the surface of merozoites in intact schizonts. Dual immunofluorescence assays with markers for the inner membrane complex (IMC) and microtubules suggest partial colocalization in both asexual and sexual stage parasites. Using the soluble recombinant PfATRP in a screen of plasma samples revealed that malaria-infected children have naturally acquired PfATRP-specific antibodies.