N-linked carbohydrate chains protect laccase III from proteolysis in Coriolus versicolor

The structure and function of the N-linked carbohydrate chains in laccase III, one of the ligninolytic glycoenzymes from the white-rot fungus Coriolus versicolor, have been partially characterized using endoglycosidases (Endo F and Endo H) and the N-asparagine-specific inhibitor, tunicamycin. In the presence of 10 μg tunicamycin ml−1 laccase and proteinase activities in culture filtrates of C. versicolor were measured over 3 weeks. Laccase activity was slightly decreased by the addition of tunicamycin, whereas proteinase activity was increased. The N-linked carbohydrate chains were not necessary for laccase secretion and activity. Endo-glycosidase digestion showed that laccase III contained at least four N-linked carbohydrate chains, of which two were high-mannose type or hybrid type and two were complex type. Judging from the differences in the resistance of the native and the carbohydrate-depleted laccase to proteolytic digestion and high temperature, the four N-linked carbohydrate chains have important protective functions against proteolytic attack and elevated temperature.