As a basic study, the fusion expressions of two functionally related proteins were described. The side by side fusion construction, expression, purification and functional characterization of Arabidopsis papain-like cysteine proteinase (CP) and cysteine proteinase inhibitor (CPI) were successfully carried out by using an Escherichia coli expression system without affecting the recombinant bacterial growth. The purification products of two different fused constructs designated as «R1: H2N-maltose binding protein-CPI-CP-COOH and R2: H2N-maltose binding protein-CP-CPI-COOH» showed inverse enzymatic/inhibitory activities, in vitro. Analysis of the constructs by using computational tools revealed that the arrangement of CP/CPI pair in fusion forms might be the important criteria for proper tertiary organization, structural folding and functional property. The overall results showed that the C-terminally located molecule could be the active folded structure in each fusion construct. The achievements of the present work may be utilized in a specific protein engineering application such as manufacturing the novel switchable expression systems in the future.
Keywords: Cysteine proteinase, Cystatin, Fusion protein, Papain