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First published online July 13, 2004
doi: 10.1242/10.1242/jcs.01198

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Calcium binding protein 1 of the protozoan parasite Entamoeba histolytica interacts with actin and is involved in cytoskeleton dynamics

¹ School of Life Sciences, Jawaharlal Nehru University, Aruna Asaf Ali Marg, New Delhi, 110067 India
² School of Environmental Sciences, Jawaharlal Nehru University, Aruna Asaf Ali Marg, New Delhi, 110067 India
³ School of Physical Sciences, Jawaharlal Nehru University, Aruna Asaf Ali Marg, New Delhi, 110067 India
⁴ Unité de Biologie Cellulaire du Parasitisme, INSERM U389, Institut Pasteur, 25-28 rue du Dr Roux, 75015 Paris, France

^* Author for correspondence (e-mail: alok0200{at}mail.jnu.ac.in)

Accepted 8 March 2004

Blocking expression of EhCaBP1, a calmodulin-like, four EF-hand protein from the protozoan parasite Entamoeba histolytica, resulted in inhibition of cellular proliferation. In this paper we report that EhCaBP1 is involved in dynamic changes of the actin cytoskeleton. Both endocytosis and phagocytosis were severely impaired in cells where EhCaBP1 expression was blocked by inducible expression of the antisense RNA. In wild-type cells both actin and EhCaBP1 were found to co-localize in phagocytic cups and in pseudopods. However, in antisense-blocked cells the phagocytic cup formation is affected. Analysis of the staining patterns in the presence and absence of actin dynamics inhibitors, jasplakinolide and cytochalasin D suggested that EhCaBP1 and polymerized F-actin co-localize on membrane protrusions. Direct interaction between soluble EhCaBP1 and F-actin was further demonstrated by a co-sedimentation assay. A variant of EhCaBP1 did not bind F-actin showing the specificity of the interaction between EhCaBP1 and actin. There is no significant change in the kinetics of in vitro polymerization of actin in presence of EhCaBP1, indicating that EhCaBP1 does not affect filament treadmilling. In addition, using atomic force microscopy; it was found that filaments of F-actin, polymerized in presence of EhCaBP1, were thinner. These results indicate that EhCaBP1 may be involved in dynamic membrane restructuring at the time of cell pseudopod formation, phagocytosis and endocytosis in a process mediated by direct binding of EhCaBP1 to actin, affecting the bundling of actin filaments.

Key words: Phagocytosis, Antisense, Actin, Atomic force microscopy, Cytoskeleton

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