Effects of engineered methionine in the 8Sα globulin of mungbean on its physicochemical and functional properties and potential nutritional quality

The major storage protein of mungbean, 8Sα globulin or vicilin, was engineered using site-directed mutagenesis to increase the number of methionine (Met) residues in the molecule for improvement of functional and nutritional qualities. Eight Met-rich proteins were designed and prepared to have 2 to 10 Met residues introduced in disordered regions II and IV. The designed proteins were highly expressed as soluble form in Escherichia coli. Their production level of the modified proteins was estimated to be about 30%, and was almost the same as that of 8Sα globulin wild type (WT). The modified proteins formed stable native conformation similar to WT as shown by gel filtration chromatography. They demonstrated greater stability in terms of thermal denaturation temperature and greater emulsifying ability and emulsion stability, especially the 10-Met protein, compared to the wild type. Met-rich proteins with 3, 5, and 10 Met residues had 74, 96, and 145% of nutritional requirement for Met compared with 41% for WT. Based on allergenicity prediction programs, WT and all the modified proteins had no allergenic potential.

► Mungbean vicilins were engineered to increase Met by site-directed mutagenesis. ► Soluble novel Met-rich proteins were expressed in Escherichia coli at high level. ► Exhibited stable trimer conformation like wild type. ► Had greater emulsifying property and thermal stability. ► Had 75–145% of nutritional requirement for Met and no allergenic potential.