A PROTEIN WITH A NOVEL CALCIUM-BINDING DOMAIN ASSOCIATED WITH CALCAREOUS CORPUSCLES IN ECHINOCOCCUS-GRANULOSUS

A novel intracellular calcium-binding protein from Echinococcus granul osus is described in this work. A cDNA was isolated from a lambda gt11 protoscolex expression library and the deduced. amino acid sequence h as at least fifteen sequentially repeated twelve-residue repeats that resemble the calcium-binding loop of EF-hands; however, the dodecamer motif has no flanking helices. The cDNA was expressed in Escherichia c oli using the pGEX vector, and a recombinant fusion protein (EgCaBP1-G ST) was obtained. The recombinant fusion protein binds calcium when as sayed with Ca-45. It is possible that the calcium-binding motifs prese nt a secondary structure similar to the parallel beta roll structure d escribed for an alkaline protease from Pseudomonas aeruginosa. A nativ e protein of more than 300 kDa was recognized by an anti-EgCaBP1 monoc lonal antibody by Western-blot analysis. Immunohistochemistry using a pool of anti-EgCaBP1-GST mouse sera demonstrated a strong association of the protein with calcareous corpuscles. The possible role of this p rotein and that of the calcareous corpuscles in the protoscolex are di scussed. (C) 1997 Academic Press.