Enzyme characterisation and gene expression profiling of Atlantic salmon chicken- and goose-type lysozymes

Lysozymes represent important innate immune components against bacteria. In this study, Atlantic salmon (Salmo salar) goose (g-) and chicken (c-) types of lysozyme were subjected to protein characterisations and tissue expression analyses. Specific bacterial protein inhibitors of g- and c-type lysozymes were employed to discriminate between respective enzyme activities. Blood, gills and liver contained activities exclusive for the g-type lysozyme. Only haematopoietic organs (head kidney and spleen) contained enzyme activities of both g- and c-lysozyme enzymes and c-type activity was not found outside these organs. Gene transcript levels proportional to enzyme activity levels were detected for the g-type lysozyme but not for the c-type. In vitro studies revealed significant induction of c-type gene expression and enzyme activity in macrophages after incubation with lipopolysaccharide (LPS) while expression of the g-type lysozyme gene was unaffected. The activity of purified native c-type enzyme was profoundly reduced by divalent cations and displayed low tolerance to monovalent cations, while the native g-type lysozyme was stimulated by monovalent cations and tolerated low concentrations of divalent cations. Activities of both enzymes increased with temperature elevations up to 60°C. The native g-type lysozyme responses to temperature in particular are in apparent conflict to the ones for the recombinant salmon g-lysozyme. Our results imply separate expression regulations and different functions of c- and g-type lysozymes in salmon. LPS-induced expression of c-type lysozyme and broad constitutive tissue distribution of g-type lysozyme in salmon is different from findings in other studied fish species.