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Structural and functional dissection of the adhesive domains of Plasmodium falciparum thrombospondin-related anonymous protein (TRAP).

ABSTRACT: TRAP (thrombospondin-related anonymous protein) is a sporozoite surface protein that plays a central role in hepatocyte invasion. We have developed procedures for recombinant production of the entire ECD (extracellular domain) and A domain of TRAP using bacterial- and baculovirus-expression systems respectively. The ECD and A domain were purified to homogeneity and migrated on gel-filtration columns as non-aggregated, monomeric proteins. These adhesive modules bound to HepG2 cells in a dose-dependent and bivalent cation-independent manner. The binding of ECD and the A domain to HepG2 cells was inhibited poorly by an excess of sulphatide analogues, suggesting the presence of as yet unidentified receptors for the A domain on hepatocytes. Using surface-plasmon-resonance-based sensor technology (Biacore), we demonstrate that TRAP ECD has higher affinity for heparin (K(D)=40 nM) compared with the A domain (K(D)=79 nM). We also present a three-dimensional structure of the A domain based on the crystal structure of the homologous von Willebrand factor A1 domain. The TRAP A domain shows two spatially distinct ligand-binding surfaces. One surface on the A domain contains the MIDAS (metal-ion-dependent adhesion site) motif, where point mutations of Thr131 and Asp162 correlate with impairment of cell infectivity by sporozoites. The other surface contains a putative heparin-binding site and consists of a basic residue cluster. Our studies suggest that TRAP interacts with multiple receptors during the hepatocyte invasion process. Our results also pave the way for inclusion of these high-quality recombinant TRAP domains in subunit-based vaccines against malaria.

SUBMITTER: Akhouri RR

PROVIDER: S-EPMC1224115 | biostudies-other | 2004 May

REPOSITORIES: biostudies-other

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Project description:BackgroundThrombospondin-related adhesive protein (TRAP) is a transmembrane protein that plays a crucial role during the invasion of Plasmodium falciparum into liver cells. As a potential malaria vaccine candidate, the genetic diversity and natural selection of PfTRAP was assessed and the global PfTRAP polymorphism pattern was described.Methods153 blood spot samples from Bioko malaria patients were collected during 2016-2018 and the target TRAP gene was amplified. Together with the sequences from database, nucleotide diversity and natural selection analysis, and the structural prediction were preformed using bioinformatical tools.ResultsA total of 119 Bioko PfTRAP sequences were amplified successfully. On Bioko Island, PfTRAP shows its high degree of genetic diversity and heterogeneity, with π value for 0.01046 and Hd for 0.99. The value of dN-dS (6.2231, p < 0.05) hinted at natural selection of PfTRAP on Bioko Island. Globally, the African PfTRAPs showed more diverse than the Asian ones, and significant genetic differentiation was discovered by the fixation index between African and Asian countries (Fst > 0.15, p < 0.05). 667 Asian isolates clustered in 136 haplotypes and 739 African isolates clustered in 528 haplotypes by network analysis. The mutations I116T, L221I, Y128F, G228V and P299S were predicted as probably damaging by PolyPhen online service, while mutations L49V, R285G, R285S, P299S and K421N would lead to a significant increase of free energy difference (ΔΔG > 1) indicated a destabilization of protein structure.ConclusionsEvidences in the present investigation supported that PfTRAP gene from Bioko Island and other malaria endemic countries is highly polymorphic (especially at T cell epitopes), which provided the genetic information background for developing an PfTRAP-based universal effective vaccine. Moreover, some mutations have been shown to be detrimental to the protein structure or function and deserve further study and continuous monitoring.

Project description:BackgroundPlasmodium knowlesi a parasite of the macaques is currently the most common cause of human malaria in Malaysia. The thrombospondin-related adhesive protein (TRAP) gene is pre-erythrocytic stage antigen. It is a well-characterized vaccine candidate in Plasmodium vivax and Plasmodium falciparum, however, no study has been done in the orthologous gene of P. knowlesi. This study investigates nucleotide diversity, haplotypes, natural selection and population differentiation of full-length pktrap genes in clinical samples from Malaysia.MethodsForty full-length pktrap sequences from clinical isolates of Malaysia along with the reference H-strain were downloaded from published databases. Genetic diversity, polymorphism, haplotype and natural selection were determined using DnaSP 5.10 software. McDonald-Kreitman test was conducted using P. vivax and Plasmodium coatneyi as ortholog sequence in DnaSP 5.10 software. Population genetic differentiation index (FST) of parasite populations was determined using Arlequin v3.5. Phylogenetic relationships between trap ortholog genes were determined using MEGA 5.0 software.ResultsComparison of 40 full-length pktrap sequences along with the H-strain identified 74 SNPs (53 non-synonymous and 21 synonymous substitutions) resulting in 29 haplotypes. Analysis of the full-length gene showed that the nucleotide diversity was lower compared to its nearest ortholog pvtrap. Domain-wise analysis indicated that the proline/asparagine rich region had higher nucleotide diversity compared to the von Willebrand factor domain and the thrombospondin-type-1 domain. McDonald-Kreitman test identified that the ratio of the number of nonsynonymous to synonymous polymorphic sites within P. knowlesi was significantly higher than that of the number of nonsynonymous to synonymous fixed sites between P. knowlesi and P. vivax. The von Willebrand factor domain also indicated balancing selection using MK test, however, it did not give significant results when tested with P. coatneyi as an outgroup. Phylogenetic analysis of full-length genes identified three distinct sub-clusters of P. knowlesi, one originating from Peninsular Malaysia and two originating from Malaysian Borneo. High population differentiation values was observed within samples from Peninsular Malaysia and Malaysian Borneo.ConclusionsThis study is the first to report on the genetic diversity and natural selection of full-length pktrap. Low level of genetic diversity was found across the full-length gene of pktrap. Balancing selection of the von Willebrand factor domain indicated that TRAP could be a target in inducing immune response against P. knowlesi infections. However, higher number of samples would be necessary to further confirm the findings.

Project description:BackgroundEmerging resistance of the malaria parasite Plasmodium to current therapies underscores the critical importance of exploring novel strategies for disease eradication. Plasmodium species are obligate intracellular protozoan parasites. They rely on an unusual form of substrate-dependent motility for their migration on and across host-cell membranes and for host cell invasion. This peculiar motility mechanism is driven by the 'glideosome', an actin-myosin associated, macromolecular complex anchored to the inner membrane complex of the parasite. Myosin A, actin, aldolase, and thrombospondin-related anonymous protein (TRAP) constitute the molecular core of the glideosome in the sporozoite, the mosquito stage that brings the infection into mammals.MethodsVirtual library screening of a large compound library against the PfAldolase-TRAP complex was used to identify candidate compounds that stabilize and prevent the disassembly of the glideosome. The mechanism of these compounds was confirmed by biochemical, biophysical and parasitological methods.ResultsA novel inhibitory effect on the parasite was achieved by stabilizing a protein-protein interaction within the glideosome components. Compound 24 disrupts the gliding and invasive capabilities of Plasmodium parasites in in vitro parasite assays. A high-resolution, ternary X-ray crystal structure of PfAldolase-TRAP in complex with compound 24 confirms the mode of interaction and serves as a platform for future ligand optimization.ConclusionThis proof-of-concept study presents a novel approach to anti-malarial drug discovery and design. By strengthening a protein-protein interaction within the parasite, an avenue towards inhibiting a previously "undruggable" target is revealed and the motility motor responsible for successful invasion of host cells is rendered inactive. This study provides new insights into the malaria parasite cell invasion machinery and convincingly demonstrates that liver cell invasion is dramatically reduced by 95 % in the presence of the small molecule stabilizer compound 24.

Project description:BackgroundThe P-loop NTPases constitute one of the largest groups of globular protein domains that play highly diverse functional roles in most of the organisms. Even with the availability of nearly 300 different Hidden Markov Models representing the P-loop NTPase superfamily, not many P-loop NTPases are known in Plasmodium falciparum. A number of characteristic attributes of the genome have resulted into the lack of knowledge about this functionally diverse, but important class of proteins.MethodIn the study, protein sequences with characteristic motifs of NTPase domain (Walker A and Walker B) are computationally extracted from the P. falciparum database. A detailed secondary structure analysis, functional classification, phylogenetic and orthology studies of the NTPase domain of repertoire of 97 P. falciparum P-loop NTPases is carried out.ResultsBased upon distinct sequence features and secondary structure profile of the P-loop domain of obtained sequences, a cladistic classification is also conceded: nucleotide kinases and GTPases, ABC and SMC family, SF1/2 helicases, AAA+ and AAA protein families. Attempts are made to identify any ortholog(s) for each of these proteins in other Plasmodium sp. as well as its vertebrate host, Homo sapiens. A number of P. falciparum P-loop NTPases that have no homologue in the host, as well as those annotated as hypothetical proteins and lack any characteristic functional domain are identified.ConclusionThe study suggests a strong correlation between sequence and secondary structure profile of P-loop domains and functional roles of these proteins and thus provides an opportunity to speculate the role of many hypothetical proteins. The study provides a methodical framework for the characterization of biologically diverse NTPases in the P. falciparum genome.The efforts made in the analysis are first of its kind; and the results augment to explore the functional role of many of these proteins from the parasite that could provide leads to identify novel drug targets against malaria.

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Structural and functional dissection of the adhesive domains of Plasmodium falciparum thrombospondin-related anonymous protein (TRAP).

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