Differential effects of D-amino acids on the fusion forms of a cysteine proteinase/cystatin pair

The interactions of 2 different fusion constructs of a plant cysteine proteinase (CP)/cysteine proteinase inhibitor (CPI) pair designated as R1: H₂N-maltose-binding protein-CPI-CP-COOH and R2: H₂N-maltose-binding protein-CP-CPI-COOH with 4 different D-amino acids including D-Ala, D-Ser, D-Asp and D-Phe were analyzed using experimental methods and computational tools. The results showed that the relative activity of CP is increased in purified R2 product and test D-amino acids tend to interact with CP/CPI pair. In contrast, the functionality of R1 product was not influenced by test D-amino acids. Determination of the effects of D-enantiomers of amino acids on the fusion forms of 2 functionally related proteins such as CP and CPI is the first research in this area. The results related to the binding abilities and the functional properties of 2 differentially organized forms of CP/CPI pair are predicted to be used as biotechnological clues to make switchable expression systems of 2 functionally related proteins in the future.