Heterologous expression of thermopsin, a heat-stable acid proteinase

We have previously reported the isolation, characterization, and gene sequence of a new thermostable acid protease, thermopsin, from Sulfolobus acidocaldarius, a thermophilic archaebacterium. Thermopsin is similar to aspartic protease pepsin in specificity and pH dependence. However, it optimally catalyzes in the temperature range of 85 to 90 degrees C and it is not structurally related to pepsin. The current report describes the synthesis of recombinant thermopsin in E. coli and in insect cells. Several recombinant thermopsin fusion proteins were expressed as "inclusion bodies" in the cytosol of E. coli. Active thermopsin preparations were obtained by refolding from urea solutions. Recombinant thermopsin was also expressed in insect cells using a baculovirus expression system. The thermostability of recombinant thermopsin is similar to that of the native enzyme.