![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Vol. 17, Issue 2, 895-906, February 2006
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
* Department of Molecular Microbiology, Center for Infectious Diseases, Washington University School of Medicine, St. Louis, MO 63110;
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110; and
Department of Biomedical Engineering, Center for Computational Biology, Washington University, St. Louis, MO 63130
Submitted June 8, 2005;
Revised October 3, 2005;
Accepted November 18, 2005
Monitoring Editor: David Drubin
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.
Abbreviations used: TgACT1, Toxoplasma actin; Cyt, cytochalasin; EM, electron microscopy; F-actin, filamentous actin; G-actin, globular actin; JAS, jasplakinolide.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
Address correspondence to: David Sibley (sibley{at}borcim.wustl.edu).
This article has been cited by other articles:
|
|
 |
|
  P. Kapoor, A. A. Sahasrabuddhe, A. Kumar, K. Mitra, M. I. Siddiqi, and C. M. Gupta An Unconventional Form of Actin in Protozoan Hemoflagellate, Leishmania J. Biol. Chem., August 15, 2008; 283(33): 22760 - 22773. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Bosch, C. A. Buscaglia, B. Krumm, B. P. Ingason, R. Lucas, C. Roach, T. Cardozo, V. Nussenzweig, and W. G. J. Hol Aldolase provides an unusual binding site for thrombospondin-related anonymous protein in the invasion machinery of the malaria parasite PNAS, April 24, 2007; 104(17): 7015 - 7020. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I. M. Sehring, C. Reiner, J. Mansfeld, H. Plattner, and R. Kissmehl A broad spectrum of actin paralogs in Paramecium tetraurelia cells display differential localization and function J. Cell Sci., January 1, 2007; 120(1): 177 - 190. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. L. Starnes, T. J. Jewett, V. B. Carruthers, and L. D. Sibley Two Separate, Conserved Acidic Amino Acid Domains within the Toxoplasma gondii MIC2 Cytoplasmic Tail Are Required for Parasite Survival J. Biol. Chem., October 13, 2006; 281(41): 30745 - 30754. [Abstract] [Full Text] [PDF]
|
|
