Abstract
Entamoeba histolytica is a protist parasite that is the causative agent of amoebiasis, and is a highly motile organism. The motility is essential for its survival and pathogenesis, and a dynamic actin cytoskeleton is required for this process. EhCoactosin, an actin-binding protein of the ADF/cofilin family, participates in actin dynamics, and here we report our studies of this protein using both structural and functional approaches. The X-ray crystal structure of EhCoactosin resembles that of human coactosin-like protein, with major differences in the distribution of surface charges and the orientation of terminal regions. According to in vitro binding assays, full-length EhCoactosin binds both F- and G-actin. Instead of acting to depolymerize or severe F-actin, EhCoactosin directly stabilizes the polymer. When EhCoactosin was visualized in E. histolytica cells using either confocal imaging or total internal reflectance microscopy, it was found to colocalize with F-actin at phagocytic cups. Over-expression of this protein stabilized F-actin and inhibited the phagocytic process. EhCoactosin appears to be an unusual type of coactosin involved in E. histolytica actin dynamics.
Highlights
Human amoebiasis is caused by the protist parasite E. histolytica
Phagocytosis and motility depend on highly dynamic actin cytoskeleton of this organism
Overexpression of this protein in trophozoites leads to stabilization of actin filaments which are not accessible to actin remodelling machinery thereby reducing the growth of parasite due to decreased rate of actin dependent endocytosis
Summary
Human amoebiasis is caused by the protist parasite E. histolytica. The parasite is highly motile and displays high level of phagocytic activity in the trophozoite stage. Motility and phagocytosis are essential processes for the survival and invasion of host tissues by the parasite, and largely depends on a highly dynamic actin cytoskeleton. Molecular mechanisms that regulate actin dynamics in E. histolytica have not been studied in detail. A number of calcium-sensing calcium-binding proteins appear to directly regulate actin recruitment and dynamics [1,2,3]. Several actin-binding proteins are encoded by the E. histolytica genome and many of these proteins are homologs of those that have been studied in other systems. Not many of these amebic actin-binding proteins have been characterized. Understanding structuralfunctional relationship of these proteins would help to decipher mechanisms of actin dynamics in E. histolytica
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