Molecular cloning and characterization of a novel ras-related protein (rap2) from Clonorchis sinensis

Ras are key components of diverse signal transduction pathways and play important roles in growth and development. To know about growth regulation in Clonorchis sinensis, we have identified a full-length sequence encoding a ras-related protein (rap2) from our adult cDNA library. The open reading frame contains 561 bp encoding 186 amino acids. The hypothetical amino acid sequence shared high identities with rap2 proteins from Schistosoma japonicum and Homo sapiens. Conserved domains of small guanosine triphosphate-binding proteins and characteristic amino acid residues of rap2 proteins were observed in this sequence. Reverse transcription polymerase chain reaction experiments revealed that rap2 transcribed in adult worm, metacercaria, and eggs of C. sinensis. Recombinant rap2 protein was expressed and purified from Escherichia coli. rap2 could be probed by C. sinensis-infected rat serum in western blotting experiment. By immunohistochemistry, rap2 was localized on the tegument of adult worm and metacercaria of C. sinensis. This fundamental study might contribute to further researches in signaling systems that are related to growth control and development of C. sinensis and other parasites.