Lysozymes (EC 3.2.1.17) are hydrolytic enzymes, characterized by their ability to cleave the β-(1,4)-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, the major bacterial cell wall polymer. In the animal kingdom, three major distinct lysozyme types have been identified — the c-type (chicken or conventional type), the g-type (goose-type) and the i-type (invertebrate type) lysozyme. Examination of the phylogenetic distribution of these lysozymes reveals that c-type lysozymes are predominantly present in the phylum of the Chordata and in different classes of the Arthropoda. Moreover, g-type lysozymes (or at least their corresponding genes) are found in members of the Chordata, as well as in some bivalve mollusks belonging to the invertebrates. In general, the latter animals are known to produce i-type lysozymes. Although the homology in primary structure for representatives of these three lysozyme types is limited, their three-dimensional structures show striking similarities. Nevertheless, some variation exists in their catalytic mechanisms and the genomic organization of their genes. Regarding their biological role, the widely recognized function of lysozymes is their contribution to antibacterial defence but, additionally, some lysozymes (belonging to different types) are known to function as digestive enzymes.

Lysozymes in the animal kingdom

Responses of midgut amylases of Helicoverpa armigera to feeding on various host plants.

Strategies for the Isolation and Characterization of Antimicrobial Peptides of Invertebrates

Genome fingerprinting in silkworm, bombyx mori, using random arbitrary primers

Lysozymes were purified from the hemolymph of three immunized Lepidopteran larvae, Galleria mellonella, Bombyx mori, Agrius convolvuli to compare their physico-chemical properties and antibacterial activities with those of chicken lysozyme. Four lysozymes including the one from chicken had similar molecular masses and chromatographic behavior on reverse phase-high pressure liquid chromatography. Western blotting analysis using an antibody raised against G. mellonella revealed that lysozyme cross-reacted with two other insect lysozymes but not with commercial chicken lysozyme. Antibacterial activities of lysozymes were measured in two types of tests: radial diffusion assay and colony count assay. Our antibacterial tests revealed that all lysozymes have strong activities against Gram-positive bacteria and three insect lysozymes still retain a little potency against Gram-negative bacteria, while chicken lysozyme has no activity against Gram-negative bacteria. Taken together, we conclude three Lepidopteran lysozymes have a common distinct structure and have an antibacterial activity, which is absent in chicken lysozyme, against Gram-negative bacteria.

Comparative study on characteristics of lysozymes from the hemolymph of three lepidopteran larvae, Galleria mellonella, Bombyx mori, Agrius convolvuli.

R.K. Datta

Papers

Biochemical studies of amylases in the silkworm, Bombyx mori L.: Comparative analysis in diapausing and nondiapausing strains

Purification and Partial Characterization of an Induced Antibacterial Protein in the Silkworm, Bombyx mori