Isolation and characterization of Cu/Zn–superoxide dismutase in Fasciola gigantica

• A cDNA coding for Fasciola gigantica Cu/Zn–superoxide dismutase (SOD) was isolated.
• Differential expression of the enzyme studied in the adult, juvenile and metacercaria.
• Recombinant Cu/Zn–SOD partially characterized for enzyme activity, pH profile in NBT–PAGE.
• Cu/Zn–SODs in the somatic and excretory secretory product of the fluke were studied.

A full-length complementary DNA (cDNA) encoding Cu/Zn–superoxide dismutase was isolated from Fasciola gigantica that on nucleotide sequencing showed a close homology (98.9%) with Cu/Zn–superoxide dismutase (SOD) of the temperate liver fluke, F. hepatica. Expression of the gene was found in all the three developmental stages of the parasite viz. adult, newly excysted juvenile and metacercaria at transcriptional level by reverse transcription-polymerase chain reaction (RT-PCR) and at the protein level by Western blotting. F. gigantica Cu/Zn–SOD cDNA was cloned and expressed in Escherichia coli. Enzyme activity of the recombinant protein was determined by nitroblue tetrazolium (NBT)–polyacrylamide gel electrophoresis (PAGE) and this activity was inactivated by hydrogen peroxide but not by sodium azide, indicating that the recombinant protein is Cu/Zn–SOD. The enzyme activity was relatively stable at a broad pH range of pH 4.0–10.0. Native Cu/Zn–superoxide dismutase protein was detected in the somatic extract and excretory–secretory products of the adult F. gigantica by Western blotting. NBT–PAGE showed a single Cu/Zn–SOD present in the somatic extract while three SODs are released ex vivo by the adult parasite. The recombinant superoxide dismutase did not react with the serum from buffaloes infected with F. gigantica. The role of this enzyme in defense by the parasite against the host reactive oxygen species is discussed.

Graphical AbstractNitro blue tetrazolium–polyacrylamide gel (NBT–PAGE) showing Fasciola gigantica recombinant Cu/Zn–superoxide dismutase enzyme activity (lane 1) and effect of various concentrations of hydrogen peroxide (lanes 2, 3 and 4) and sodium azide (lanes 5, 6 and 7) on the Cu/Zn–SOD enzyme activity.Figure optionsDownload as PowerPoint slide