Lysozyme, an important secretory innate immune component, possesses antimicrobial activity against broad spectrum of bacteria and viruses. In the present study, complete CDs (558 bps) of g-type lysozyme of rohu (Labeo rohita) was amplified and translated for a putative protein of 185 amino acids. The domain architecture and tertiary structure was also predicted for the protein. Its expression profile was studied in three infection models (bacteria: Aeromonas hydrophila, poly I:C, a dsRNA viral analogue and an ectoparasite: Argulus siamensis) in liver and kidney tissues of rohu. An up-regulation of 630-fold and 420-fold of the gene was observed at 48 h in liver and anterior kidney tissues respectively, after A. hydrophila infection. Significant increase in transcript level was noticed in both liver (0.8-fold) and kidney (480-fold) after 1 h and 12 h of poly I:C induction, respectively. Similarly, expression of lysozyme g transcripts was increased 6000-fold after 7 d of A. siamensis infection in liver tissue. The recombinant protein of g-type lysozyme of rohu (rLr-lysG) of 20.19 kDa was produced in Escherichia coli system and the lysozyme activity of rLr-lysG was found to be most active at pH 6.0 and temperature 35 °C. The potential lytic activity was found to be against A. hydrophila (UL = 0.53) followed by for E. tarda (UL = 0.45) whereas the lytic activity was the least against S. aureus (UL = 0.35) and M. lysodeikticus (UL = 0.34), at pH 6.0 and temperature 35 °C. The normal serum level of protein was estimated using indirect ELISA and was found to be very low (0.12-0.15 μg/ml). These results suggested that g-type lysozyme of rohu might be a potent immunostimulant against microbial infections, with a major role in innate immunity.
Keywords: Antimicrobial property; Expression analysis; G-type lysozyme; Immunostimulant; Indirect ELISA; Labeo rohita.
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