An EF-handed Ca(2+)-binding protein of Chinese liver fluke Clonorchis sinensis

A cDNA clone encoding 8 kDa protein was retrieved from an EST pool of Chinese liver fluke Clonorchis sinensis. A deduced polypeptide of the cDNA clone was similar to 8 kDa Ca(2+)-binding proteins from other parasitic trematodes, and, thus, named as CsCa8, containing two EF-hand Ca(2+)-binding sites. Homology models predicted CsCa8 to be a single globular structure having four helices and molecular folds similar to Ca(2+)-binding state of other small Ca(2+)-binding proteins. Recombinant CsCa8 protein showed specific Ca(2+)-binding affinity and shifting in native gel mobility assay. Mouse immune sera raised against recombinant CsCa8 protein recognized native CsCa8 from adult C. sinensis worm extract. CsCa8 was localized in oral and ventral suckers, vitelline follicles and subtegumental tissues. These findings suggest that CsCa8 might be involved in cellular Ca(2+) signal transduction for muscle contraction and egg production.