Molecular cloning and functional analysis of HnSaratin from Hirudo nipponia

In order to finish a bloodmeal successfully, hematophagous organisms often stored a variety of anticoagulant proteins in their salivary glands, such as proteins that inhibit platelet aggregation. When they ingest a bloodmeal, these proteins are injected into the host to prevent the blood from clotting. As one of the origins of leeches used in traditional Chinese medicine, H. nipponia was proved to be clinically effective in treatment of cardiovascular and cerebrovascular diseases. This study cloned the sequence of HnSaratin cDNA derived from salivary glands of H. nipponia. The sequence contains an open reading frame of 387 bp, encoding a protein of 128 amino acids containing a signal peptide of 21 amino acids. After removal of the signal peptide, the molecular mass of mature HnSaratin was 12.37 kDa, with a theoretical isoelectric point (pI) of 3.89. The N-terminal of mature HnSaratin was folded into a globular structure, in which 3 disulfide bonds, a ββαβββ topology and 2 Glu residues that binds collagenous Lys2 were located, and the C-terminal formed a flexible region. The fusion HnSaratin protein was obtained by a prokaryotic expression system. The protein showed anti-platelet aggregation activity, and was observed to prevent blood clotting in rats. The significant high expression of HnSaratin mRNA in salivary glands was induced by bloodmeal ingestion of H. nipponia. Briefly, our work provides theoretical basis for further development and utilization of H. nipponia.