Monitoring global gene expression of proteases and improvement of human lysozyme production in the nptB gene disruptant of Aspergillus oryzae

Aspergillus oryzae has numerous protease genes that might cause proteolytic degradation of heterologously-produced proteins. The productivity of the heterologous protein can be improved by protease gene disruption, but it is difficult to select disruption targets efficiently. In this study, we monitored the expression of 132 protease genes by DNA microarray. A group of protease genes up-regulated during cultivation was identified by clustering analysis. In this protease group, the nptB gene encoding neutral protease II was included as well as the alpA, tppA, and pepA genes, disruption of which has improved human lysozyme (HLY) production. The nptB gene was disrupted to investigate its involvement in HLY production, and nptB disruptants showed an improvement in the production. These observations suggest that monitoring the expression of protease genes is an efficient strategy in screening potential disruption targets for heterologous protein production in A. oryzae.