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Functional characterization of a redundant Plasmodium TRAP family invasin, TRAP-like protein, by aldolase binding and a genetic complementation test.

ABSTRACT: Efficient and specific host cell entry is of exquisite importance for intracellular pathogens. Parasites of the phylum Apicomplexa are highly motile and actively enter host cells. These functions are mediated by type I transmembrane invasins of the TRAP family that link an extracellular recognition event to the parasite actin-myosin motor machinery. We systematically tested potential parasite invasins for binding to the actin bridging molecule aldolase and complementation of the vital cytoplasmic domain of the sporozoite invasin TRAP. We show that the ookinete invasin CTRP and a novel, structurally related protein, termed TRAP-like protein (TLP), are functional members of the TRAP family. Although TLP is expressed in invasive stages, targeted gene disruption revealed a nonvital role during life cycle progression. This is the first genetic analysis of TLP, encoding a redundant TRAP family invasin, in the malaria parasite.

SUBMITTER: Heiss K

PROVIDER: S-EPMC2446664 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature

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Functional characterization of a redundant Plasmodium TRAP family invasin, TRAP-like protein, by aldolase binding and a genetic complementation test.

Heiss Kirsten K Nie Hui H Kumar Sumit S Daly Thomas M TM Bergman Lawrence W LW Matuschewski Kai K

Eukaryotic cell 20080425 6

Efficient and specific host cell entry is of exquisite importance for intracellular pathogens. Parasites of the phylum Apicomplexa are highly motile and actively enter host cells. These functions are mediated by type I transmembrane invasins of the TRAP family that link an extracellular recognition event to the parasite actin-myosin motor machinery. We systematically tested potential parasite invasins for binding to the actin bridging molecule aldolase and complementation of the vital cytoplasmi ...[more]

PMID: 18441124

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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:Aldolase has been implicated as a protein coupling the actomyosin motor and cell surface adhesins involved in motility and host cell invasion in the human malaria parasite Plasmodium falciparum. It binds to the cytoplasmic domain (CTD) of type 1 membrane proteins of the thrombospondin-related anonymous protein (TRAP) family. Other type 1 membrane proteins located in the apical organelles of merozoites, the form of the parasite that invades red blood cells, including apical membrane antigen 1 (AMA1) and members of the erythrocyte binding ligand (EBL) and reticulocyte binding homologue (RH) protein families have been implicated in host cell binding and invasion. Using a direct binding method we confirm that TRAP and merozoite TRAP (MTRAP) bind aldolase and show that the interaction is mediated by more than just the C-terminal six amino acid residues identified previously. Single amino acid substitutions in the MTRAP CTD abolished binding to aldolase. The CTDs of AMA1 and members of the EBL and RH protein families also bound to aldolase. MTRAP competed with AMA1 and RH4 for binding to aldolase, indicating overlapping binding sites. MTRAP CTD was phosphorylated in vitro by both calcium dependent kinase 1 (CDPK1) and protein kinase A, and this modification increased the affinity of binding to aldolase by ten-fold. Phosphorylation of the CTD of members of the EBL and RH protein families also increased their affinity for aldolase in some cases. To examine whether or not MTRAP expressed in asexual blood stage parasites is phosphorylated, it was tagged with GFP, purified and analysed, however no phosphorylation was detected. We propose that CTD binding to aldolase may be dynamically modulated by phosphorylation, and there may be competition for aldolase binding between different CTDs. The use and efficiency of alternate invasion pathways may be determined by the affinity of adhesins and cell invasion proteins for aldolase, in addition to their host ligand specificity.

Dataset Information

Functional characterization of a redundant Plasmodium TRAP family invasin, TRAP-like protein, by aldolase binding and a genetic complementation test.

Publications

Functional characterization of a redundant Plasmodium TRAP family invasin, TRAP-like protein, by aldolase binding and a genetic complementation test.

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