FhCaBP1 (FH22): A Fasciola hepatica calcium-binding protein with EF-hand and dynein light chain domains.

FH22 has been previously identified as a calcium-binding protein from the common liver fluke, Fasciola hepatica. It is part of a family of at least four proteins in this organism which combine an EF-hand containing N-terminal domain with a C-terminal dynein light chain-like domain. Here we report further biochemical properties of FH22, which we propose should be renamed FhCaBP1 for consistency with other family members. Molecular modelling predicted that the two domains are linked by a flexible region and that the second EF-hand in the N-terminal domain is most likely the calcium ion binding site. Native gel electrophoresis demonstrated that the protein binds both calcium and manganese ions, but not cadmium, magnesium, strontium, barium, cobalt, copper(II), iron (II), nickel, zinc, lead or potassium ions. Calcium ion binding alters the conformation of the protein and increases its stability towards thermal denaturation. FhCaBP1 is a dimer in solution and calcium ions have no detectable effect on the protein's ability to dimerise. FhCaBP1 binds to the calmodulin antagonists trifluoperazine and chlorpromazine. Overall, the FhCaBP1's biochemical properties are most similar to FhCaBP2 a fact consistent with the close sequence and predicted structural similarity between the two proteins.