Abstract
BackgroundEchinococcus granulosus is a harmful cestode parasite that causes cystic echinococcosis in humans as well as various livestock species and wild animals. Calmodulin (CaM), a Ca2+ sensor protein, is widely expressed in eukaryotes and mediates a variety of cellular signaling activities.MethodsIn the present study, the cDNA encoding CaM in Echinococcus granulosus (rEgCaM) was successfully cloned and the molecular and biochemical characterizations carried out. The antigenicity and immunoreactivity of rEgCaM was detected and the preliminary enzyme-linked immunosorbent assay (ELISA)-based serodiagnostic potential of EgCaM was assessed. The locations of this protein in the adult worm and larval stage, and the mRNA expression in different states of E. granulosus protoscoleces (PSCs) were defined clearly. Moreover, the Ca2+-binding properties of EgCaM were measured.ResultsrEgCaM is a highly conserved calcium-binding protein, consisting of 149 amino acids. Immunoblotting analysis revealed that rEgCaM could be identified using E. granulosus infected sheep serum. The use of rEgCaM as an antigen was evaluated by indirect ELISA which exhibited a high sensitivity (90.3%), but low specificity (47.1%). rEgCaM was ubiquitously expressed in protoscoleces and adults of E. granulosus, as well as in the germinal layer of the cyst wall. The mRNA expression level of rEgCaM was increased from the start of H2O2 exposure and then gradually decreased because of the increased apoptosis of PSCs. In electrophoretic mobility tests and 1-anilinonaphthalene-8-sulfonic acid assays, rEgCaM showed a typical characteristic of a calcium-binding protein.ConclusionsTo our knowledge, this is the first report on CaM from E. granulosus and rEgCaM is likely to be involved in some important biological function of E. granulosus as a calcium-binding protein.
Highlights
Echinococcus granulosus is a harmful cestode parasite that causes cystic echinococcosis in humans as well as various livestock species and wild animals
BLASTp showed that the amino acid sequence of E. granulosus calmodulin (EgCaM) shared 84.9–100% identity with CaMs from E. multilocularis, Hymenolepis microstoma, Fasciola hepatica, Schistosoma japonicum, Caenorhabditis elegans, Toxocara canis, Plasmodium falciparum, Trypanosoma cruzi, Homo sapiens and Mus musculus (Fig. 1)
A phylogenetic tree showed the relationship of EgCaM with calmodulin from other parasites and hosts; EgCaM clustered with the calmodulins from E. multilocularis and H. microstoma, but not with the other calmodulins (Fig. 2)
Summary
Echinococcus granulosus is a harmful cestode parasite that causes cystic echinococcosis in humans as well as various livestock species and wild animals. Calmodulin (CaM), a Ca2+ sensor protein, is widely expressed in eukaryotes and mediates a variety of cellular signaling activities. Cystic echinococcosis (CE), called hydatid disease, is a serious zoonotic parasitic disease caused by the larval form of Echinococcus granulosus and is an important public health issue in both developed and developing countries [1, 2]. Calmodulin (CaM), a small calcium sensor protein, is one of the most evolutionarily ancient proteins in eukaryotes [5]. The functions of CaM include Ca2+ binding and conversion of Ca2+ signals though downstream proteins to regulate various physiological processes, such as muscle contraction, metabolism and cell motility [6, 7]. In Caenorhabditis elegans, 56 Ca2+-bound-calmodulin binding proteins were identified using mRNA-display, including heat shock proteins, myosin family members, CaM-dependent kinases, protein phosphatases and phosphodiesterases [12]
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