PANCREATIC RIBONUCLEASE (RNASE1) WITH DIGESTIVE AND ANTIMICROBIAL FUNCTIONS IN HERBIVOROUS Megalobrama amblycephala  

Pancreatic ribonuclease (RNase1), an important digestive enzyme, has been used as a model protein with which to study the molecular evolutionary and physiological functions of mammals. Here, we identified the RNase1 genes from five fish species and characterized the expression and function of RNase1 in the herbivorous Megalobrama amblycephala. The five identified fish RNase1 genes all have the signature motifs of the RNase A superfamily: CKXXNTF, six conserved cysteines, and the catalytic histidine-lysine-histidine triad. M. amblycephala RNase1 (Ma-RNase1) was weakly expressed in the early developmental stages and strongly expressed in the adult liver and spleen. A biological functional analysis of the recombinant protein demonstrated that Ma-RNase1 had a relatively strong ribonuclease activity at its optimal pH 6.1, which is consistent with the pH of its intestinal microenvironment. Ma-RNase1 also exhibited potent antimicrobial activity against the Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis. These results, together with the presence of ribonuclease activity in mammals RNase1 and bactericidal activity in other teleosts, strongly suggest that Ma-RNase1 has both digestive and antimicrobial activities and that these functions result from its adaptive diversification during the evolution of the species.