Expression and characterization of lactate dehydrogenase from Schistosoma japonicum

Some effective antiparasitic drugs for chemotherapy schistosomiasis, such as praziquantel and artemether, are proved to act on lactate dehydrogenase (LDH) in vitro, but detailed molecular action mechanisms of these have not yet been elucidated. To this end, the sequence encoding LDH of Schistosoma japonicum (SjLDH) was amplified from the cDNA library of the adult parasite. Sequence analysis revealed an open reading frame (ORF) of 999 bp, encoding 332 amino acids with a molecular weight of 36.120 kDa. It has three transmembrane regions and may be located in the cytoplasm membrane. The encoding ORF was inserted into pET-28a vector and expressed in Escherichia coli (E. coli) induced by IPTG. A 36-kDa protein with 6xHis-tag was purified by metal affinity column and identified by SDS-PAGE and Western blot, which had high LDH activity of 379 U/mg. Characterization such as Michaelis constant (K (m)) and maximum velocity (V (max)), optimum pH, and temperature of the protein were assayed. It provides a model for drug screening on SjLDH.