Growth promoting activity of Pangasianodon hypophthalmus recombinant growth hormone expressed in Escherichia coli

Recombinant growth hormone of Pangasianodon hypophthalmus (rPhGH) was efficiently expressed in Escherichia coli BL 21 (DE3) cells. The expression vector pET-32a(+) was used to clone and express a 550 bp long cDNA fragment, which encodes the mature region of growth hormone. The rPhGH was expressed as a 6X HIS-tag fusion protein in E. coli upon induction by Isopropyl b-D-thiogalactoside, and formed insoluble inclusion bodies in the host cells. SDS-PAGE analysis indicated that the molecular weight of the fusion protein was about 23 kDa, which is comparable to the theoretical value of the mature growth hormone of the fish. The expressed protein was recovered by solubilising the inclusion bodies under denaturing conditions with urea and then the denatured proteins were refolded and purified on Ni-NTA column. The purified recombinant protein was confirmed by Western blot analysis using anti-His antibodies. Total yield of the refolded and purified protein was 20 mg l-1 of LB medium. Biological activity of the purified recombinant protein was determined in in vivo bioassay by its ability to promote growth in rohu (Labeo rohita) fingerlings, injected with three different concentrations of the hormone. A significant increase in growth was observed in rohu fingerlings administered with rPhGH at a dosage of 1.0 mg g body weight -1.