Production of an invertebrate lysozyme of Scylla paramamosain in E. coli and evaluation of its antibacterial, antioxidant and anti-inflammatory effects

Lysozymes, which are secreted in many organisms, including invertebrates, mammals, plants, bacteria and fungus, exhibit antimicrobial, antiviral, antioxidant, and anti-inflammatory activities. Splys-i is an invertebratetype (i-type) lysozyme isolated from Scylla paramamosain in 2017 and is involved in immune defense against bacteria. However, the antibacterial, antioxidant, and anti-inflammatory activities of Splys-i remain to be elucidated. In the current study, the expression parameters (including IPTG concentration, induction temperature, and induction duration) of Splys-i in Escherichia coli were optimized to achieve high-level yield through shake-flask cultivation with approximately 120 mg of Splys-i obtained from 1 L of LB medium. The purified Splys-i displayed low cytotoxicity to RAW264.7 macrophage cells and low hemolytic activity against erythrocytes of mouse, rat, and rabbit, respectively, and exhibited potent antibacterial activity against both Grampositive and -negative bacteria with minimum concentrations ranging from 15 to 90 mu g/mL. The antibacterial property of Splys-i was also unaffected when treated with various temperature, pHs, and salinity, respectively, and Splys-i showed resistance to proteinase digestion. Radical-scavenging rate assay (including ABTS(+), DPPH, hydroyl free radical, and superoxide anion) indicated that Splys-i was an efficient antioxidant. Splys-i also exerted anti-inflammatory effect through the inhibition of I kappa B alpha and NF-kappa B(P65) phosphorylation, thereby reducing the secretion of pro-inflammatory cytokines. All these results suggested that Splys-i can be prepared from E. coli with potent biological property.