Molecular cloning, inducible expression and antibacterial analysis of a novel i-type lysozyme (lyz-i2) in Pacific white shrimp, Litopenaeus vannamei

• We identified the cDNA coding for a novel invertebrate (i-type) lysozyme in white shrimp.
• Litopenaeus vannamei lyz-i2 shares low sequence homologies with the known lyz-c and lyz-i1.
• L. vannamei lyz-i2 mRNA were detected in all our selected tissues.
• L. vannamei lyz-i2 mRNA are up-regulated by Vibiro and LPS but not Poly (I:C) challenge in hemolymph.
• We demonstrated a broad spectrum of antimicrobial activities of L. vannamei r-lyz-i2 protein.

The full-length cDNA coding for a novel invertebrate (i-type) lysozyme was identified in Pacific white shrimp (Litopenaeus vannamei). The newly obtained L. vannamei lysozyme is similar to the Penaeus monodon i-type lysozyme 2, but it is distant from the known L. vannamei c-type lysozyme and i-type lysozyme 1 in protein sequence; therefore, it was defined as L. vannamei i-type lysozyme 2 (lyz-i2). Expression of L. vannamei lyz-i2 transcripts were ubiquitously detected in all tissues we selected, with the highest abundance observed in the hemolymph. Challenge with Vibrio harveyi might elicit L. vannamei lyz-i2 mRNA expression in the hepatopancreas, intestine, muscle, gill and hemolymph. In the themolymph, specifically, the stimulatory effects of Vibrio and lipopolysaccharide (LPS) on lyz-i2 transcript levels were durable and transient, respectively; while Polyinosinic:polycytidylic acid [Poly (I:C)] treatment did not affect lyz-i2 expression. L. vannamei lyz-i2 recombinant protein was generated in an Escherichia coli system. By lysoplate and turbidimetric assays, the L. vannamei lyz-i2 recombinant protein showed a broad spectrum of antimicrobial properties with high activities against Micrococcaceae lysodeikticus and various Vibrio species and relatively low activity against E. coli. In conclusion, L. vannamei lyz-i2 might be a potent antibacterial protein with a role in innate immunity in Penaeid shrimp.