Identification and characterization of a novel goose-type and chicken-type lysozyme genes in Chinese rare minnow (Gobiocypris rarus) with potent antimicrobial activity.

Lysozymes act as important innate immunity molecule against various pathogen infections. In the present study, a new c-type and g-type lysozymes were isolated from rare minnow Gobiocypris rarus. The deduced amino acid sequence of c-type lysozyme contained 145 residues and possessed conserved catalytic residues (Glu and Asp). The deduced g-type lysozyme contained 185 residues and possessed three conserved catalytic residues (Glu, Asp and Asp). qPCR analysis revealed that GrlysG and GrlysC were constitutively expressed in all examined tissues. GrlysG was most abundant in kidney and liver, while GrlysC was predominantly expressed in liver. The transcripts of GrlysG and GrlysC genes could be significantly up-regulated after Aeromonas hydrophila and poly I:C infection in the kidney and liver. The recombinant GrlysG and GrlysC proteins were successfully produced and purified. The optimal pH and temperature for rGrlysG and rGrlysC protein lytic activities was determined to be 6.5 and 32 °C, respectively. From the minimal inhibitory concentration test, the rGrlysG and rGrlysC exhibited apparent antibacterial activities against both Gram-positive and Gram-negative bacteria at different concentrations. In conclusion, the present study indicated that c-type and g-type lysozymes participated the innate immune response to A. hydrophila and virus infections in fish.