Abstract
Simple SummaryAs a medicinal insect, Coridius chinensis contains many active polypeptides. Extracts from C. chinensis are usually complex and it is not clear which polypeptides are effective medicinal ingredients. In addition, we also need to figure out the functions of various immune effectors in the innate immunity of C. chinensis. To explore the function of lysozyme in C. chinensis, a lysozyme gene CcLys2 was screened and identified from the transcriptome data of C. chinensis. The results showed that CcLys2 had a typical domain of the c-type lysozyme, belonging to the H-branch of the c-type lysozyme. The lysozyme Cclys2 is an effective immune effector in the immune response of C. chinensis and can be stimulated by bacterial infection. Like typical c-type lysozyme, Cclys2 has lytic activity against Gram-positive bacteria. The research holds promise for functional annotation of similar proteins from other dinidoridae insects and provides the theoretical feasibility for the development of medicinal components in C. chinensis. Our results also provide data for further investigating the origin and evolution of insect lysozymes.Coridius chinensis is a valuable medicinal insect resource in China. Previous studies have indicated that the antibacterial and anticancer effects of the C. chinensis extract mainly come from the active polypeptides. Lysozyme is an effective immune effector in insect innate immunity and usually has excellent bactericidal effects. There are two kinds of lysozymes in insects, c-type and i-type, which play an important role in innate immunity and intestinal digestion. Studying lysozyme in C. chinensis will be helpful to further explore the evolutionary relationship and functional differences among lysozymes of various species and to determine whether they have biological activity and medicinal value. In this study, a lysozyme CcLys2 was identified from C. chinensis. CcLys2 contains 223 amino acid residues, and possesses a typical domain of the c-type lysozyme and a putative catalytic site formed by two conserved residues Glu32 and Asp50. Phylogenetic analysis showed that CcLys2 belongs to the H-branch of the c-type lysozyme. The analysis of spatiotemporal expression patterns indicated that CcLys2 was mainly expressed in the fat body of C. chinensis adults and was highly expressed in the second- and fifth-instar nymphs. In addition, CcLys2 was significantly up-regulated after injecting and feeding bacteria. In the bacterial inhibition assay, it was found that CcLys2 had antibacterial activity against Gram-positive bacteria at a low pH. These results indicate that CcLys2 has muramidase activity, involves in the innate immunity of C. chinensis, and is also closely related to the bacterial immune defense or digestive function of the intestine.
Highlights
Lysozyme was first discovered in human tears and saliva, and was found to dissolve bacterial cell walls and to kill bacteria
The mature peptide of CcLys2 has catalytically essential residues, glutamic E32 and aspartic D50, which are equivalent to E33 and D50 of lysozyme BmLZ in B. mori, but differs from the non-catalytic lysozyme-like proteins (LLPs), ALLP1 and BLLP1; CcLys2 is likely to have catalytic activity
A lysozyme in C. chinensis was identified by heterologous expression
Summary
Lysozyme was first discovered in human tears and saliva, and was found to dissolve bacterial cell walls and to kill bacteria. The main lysozymes identified are c-type and i-type lysozymes in insects. The i-type lysozymes have muramidase and isopeptidase activities, but the i-type lysozymes in insects lack muramidase activity. Some i-type lysozymes cannot be induced by immune stimulation, which indicates that they may have acquired new and undetermined functions in the process of evolution [12]. C-type lysozymes 1 and 2 from Musca domestica have digestive functions, which aid in the use of bacteria as a food source. These lysozymes have high expression in the gut and optimal lytic activity at a lower pH [13,14]
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