Molecular characterization of voltage-gated calcium channel β-subunits of Clonorchis sinensis

The voltage-gated Ca2+ channel beta-subunit is a member of the membrane-associated guanylate kinase family and modulates kinetic properties of the Ca2+ channels, such as their voltage-dependent activation and inactivation rates. Two cDNA clones were identified to encode each beta-subunit isotype of the voltage-gated Ca2+ channel of Clonorchis sinensis, CsCav beta 1 and CsCav beta 2, which consist of 606 and 887 amino acids, respectively. CsCav beta 1 was found to be similar to the beta-subunit containing two conserved serine residues that constitute the consensus protein kinase C phosphorylation site in the beta-interaction domain (BID). CsCav beta 2 had cysteine and alanine residues instead of the two serine residues conserved in BID and was homologous to variant beta-subunit of Schistosoma mansoni and Schistosoma japonicum. CsCav beta 1 and CsCav beta 2 were almost equally expressed in the adults and metacercariae, but were more expressed in adult C. sinensis than in metacercariae. Collectively, our findings suggest that substitution of the two serine residues in BID of CsCav beta 2 may render C. sinensis sensitive to praziquantel.