Expression and immunological characterization of the heat shock protein-70 homologue from Babesia bigemina.

The Babesia bigemina heat shock protein-70 gene (BbigHSP-70) was cloned from cDNA by polymerase chain reaction (PCR) and sequenced. The length of the gene is 1947 bp and the predicted polypeptide is 649 amino acids long with a calculated molecular weight of 70.85 kDa. BbigHSP-70 has a signal peptide of 15 amino acids. Phylogenetic analysis of the amino acid sequence of BbigHSP-70 showed that B. bigemina was most closely related to B. caballi and B. bovis and lies within a phylogenetic cluster with Theileria. rBbigHSP-70 was expressed in E. coli as a soluble GST-fusion protein with a molecular mass of 96.8-kDa. The serum raised in mice against rBbigHSP-70 detected the native protein in B. bigemina, B. bovis, B. caballi, B. gibsoni, and B. microti lysates and also reacted with B. bigemina, B. bovis, and B. caballi merozoites in the IFAT. Mice vaccinated with rBbigHSP-70 showed lower parasitemia against the challenge infection with B. microti than GST-vaccinated and non-vaccinated controls. These results added a new member of Babesia heat shock proteins70 that is well conserved among intraerythrocytic protozoa and demonstrated its protective effects in an experimental model of rodent babesiosis.