Tick lysozymes

Ticks are blood feeding arthropod parasites transmitting a wide variety of pathogens to their vertebrate hosts. The vector capability of ticks is tightly linked to their immune system. Ticks can defend themselves against microbial infection with a variety of antimicrobial peptides comprising lysozymes, defensins, and unique molecules not found in other arthropods. Lysozymes are hydrolytic enzymes, characterized by their ability to cleave the β-(1, 4)-glycosidic bond between Nacetylmuramic acid and N-acetyglucosamine in peptidoglycan, the major bacterial cell wall polymer. A full-length cDNA encoding lysozymes was obtained from cDNA libraries of salivary glands of the ixodid hard tick Haemaphysalis longicornis and designated as HlLysozyme. The HlLysozyme sequence represents an open reading frame for a putative signal peptide and the mature protein composed of 121 amino acids. The calculated molecular weight of the protein is 13.7 kDa, and the theoretical isoelectric point is 9.85. HlLysozyme shares a 41-79% amino acid sequence identity with the lysozymes of other organisms. Elevated gene expression of HlLysozyme was observed when female ticks were challenged with bacteria, suggesting the possible roles of lysozymes in the innate immunity of ticks against microorganisms. This study would provide a starting point for an immunological examination of tick-pathogen interactions.