Unusual kinetic and structural properties control rapid assembly and turnover of actin in the parasite Toxoplasma gondii

Toxoplasma is a protozoan parasite in the phylum Apicomplexa, which contains a number of medically important parasites that rely on a highly unusual form of motility termed gliding to actively penetrate their host cells. Parasite actin filaments regulate gliding motility, yet paradoxically filamento...

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Bibliographic Details
Published in:Molecular biology of the cell 2006-02, Vol.17 (2), p.895-906
Main Authors: Sahoo, Nivedita, Beatty, Wandy, Heuser, John, Sept, David, Sibley, L David
Format: Article
Language:English
Subjects:
Actin Cytoskeleton - metabolism
Actin Cytoskeleton - ultrastructure
Actins - chemistry
Actins - metabolism
Actins - ultrastructure
Animals
Apicomplexa
Baculoviridae - genetics
Baculovirus
Cells, Cultured
Cloning, Molecular
Depsipeptides - pharmacology
Kinetics
Models, Molecular
Phylogeny
Protein Structure, Tertiary
Protozoan Proteins - chemistry
Protozoan Proteins - metabolism
Protozoan Proteins - ultrastructure
Rabbits
Toxoplasma - drug effects
Toxoplasma - metabolism
Toxoplasma - ultrastructure
Toxoplasma gondii
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Summary:Toxoplasma is a protozoan parasite in the phylum Apicomplexa, which contains a number of medically important parasites that rely on a highly unusual form of motility termed gliding to actively penetrate their host cells. Parasite actin filaments regulate gliding motility, yet paradoxically filamentous actin is rarely detected in these parasites. To investigate the kinetics of this unusual parasite actin, we expressed TgACT1 in baculovirus and purified it to homogeneity. Biochemical analysis showed that Toxoplasma actin (TgACT1) rapidly polymerized into filaments at a critical concentration that was 3-4-fold lower than conventional actins, yet it failed to copolymerize with mammalian actin. Electron microscopic analysis revealed that TgACT1 filaments were 10 times shorter and less stable than rabbit actin. Phylogenetic comparison of actins revealed a limited number of apicomplexan-specific residues that likely govern the unusual behavior of parasite actin. Molecular modeling identified several key alterations that affect interactions between monomers and that are predicted to destabilize filaments. Our findings suggest that conserved molecular differences in parasite actin favor rapid cycles of assembly and disassembly that govern the unusual form of gliding motility utilized by apicomplexans.
ISSN:1059-1524
1939-4586
1059-1524
DOI:10.1091/mbc.E05-06-0512