Cloning and characterization of a cDNA clone encoding troponin T from tick Haemaphysalis qinghaiensis (Acari: Ixodidae)

Troponin T (TnT) is a key protein for Ca(2+)-sensitive molecular switching of muscle contraction. The entire cDNA sequence of Haemaphysalis qinghaiensis troponin T gene (HqTnT) from the hard tick was cloned here. The cDNA sequence of HqTnT possesses an ORF of 1170 bp coding for a mature protein with 389 amino acid residues and a molecular mass of 46.5 kDa. Search of the cloned sequence in GenBank revealed that HqTnT gene shared some homology with TnT genes of other organisms. By sequence comparison, two conserved domains were identified in the middle (residues 54-78) and close to the carboxyl-terminal end (residues 181-229) of the amino acid sequence of HqTnT. These conserved domains might be responsible for the interaction with tick tropomyosin and troponin I subunit, respectively. Reverse transcription-polymerase chain reaction showed a ubiquitous expression of HqTnT gene at different developmental stages and in different tissues of the tick. The HqTnT was expressed as glutathione S-transferase fused protein in a prokaryotic system. Though rHqTnT could induce specific antibodies in sheep, the antibodies could not protect sheep from the infestation of ticks. Therefore, recombinantly produced HqTnT could not be a candidate antigen for developing anti-tick vaccine. To our knowledge, this is the first report of tick TnT gene.